High Vacuum Reading At Idle

Doing The Vacuum Test:. A vacuum gauge is an invaluable resource for tracking down engine issues. This is information on how to set your idle rpm. There is a calculation to test your MAF sensor accuracy/efficiency and if below 95% efficiency is deemed faulty or recommend. When people talk about how much vacuum they have at idle, does the rpm you idle at matter ? I always read about how a big cam will give you lower vacuum numbers at idle. If the engine is operating under light or no load and low or closed throttle, there is high manifold vacuum. This occurs under high engine loads such as full throttle. 14 inches of vacuum at idle. High vacuum readings (25″ +) at idle are generally a sign that your engine is working hard to get air/fuel into the engine. High idle/low idle what gives! The Harmonizer is a POS that only measures vacuum pulses, not power, so it doesn't work at all. In this video I will show you how to use Idle Air Control (IAC) position to identify a vacuum leak. I'm getting excellent vacuum at idle (21 inHg). This information is from various sources, like my experience, AFM, the Ford Fuel Injection Book, other site members experiences. I take ABSOLUTELY ZERO CREDIT for the length of material you're about to read, however I have made a few comments in-text that you can see which I will highlight in green. I have a 95' with a high idle (1700 rpm), hooked up the OBD and it said TPC had a voltage problem, replaced TPC. Read real discussions on thousands of topics and get your questions answered. barometric reading is 94. We let it idle for about 10 minutes then like clockwork, the idle rpm picked up to about 1200 and the ESS warning light illuminated. If the reading is low, check to see if the vacuum hose is kinked, clogged or cracked. The plenum chambers can also chafe vacuum lines. During idle, intake manifold vacuum is at its highest. What can cause lack of manifold vacuum? HELP!! vacuum which is reading 6 inches of vacuum at idle (should be 15 to 20). MB M110 Engine Vacuum Connects - Free download as PDF File (. The maf # seems a little high to me. 0 1000rpm, standby vacuum off: Reading proper, suction 5. This definition is referring to a high or hard vacuum. common causes of rough idle, hesitation, stalling and hard starting. The truck is stock. Step 1 – Vacuum leaks or air intake leaks. One type is known as "full" vacuum or "manifold" vacuum. then turn the screws richer a slight amount. You have a severely overcharged system. Symptoms when cold or hot:- Very little power between 1000 and 2000 RPM in any gear after 2k will red line with ease, even pulling away from the lights little power till 2k and then full power…. i think i have a vacuum leak. I want a Radical Sounding Cam, What Should I Run? Well, this is a big issue and a LOT needs to be considered. 20 in gear at idle. With the secondary throttle stop set, the idle mixture screws should be more responsive. Fundamentals of Vacuum For a deeper look at vacuum systems, read "Putting vacuum to work," "Squeeze energy savings from pneumatic systems," ";Handling vacuum design," and "Designing with vacuum and suction cups. The idle of a car engine is kind of like a human heartbeat: You can tell what shape it's in just by listening. and LLY, or 0 PSI LBZ and LMM. Just some quick research on MAP sensors. The reason 272s have a lower vacum reading at idle, is because of cam overlap. High idle, rough idle What causes a high idle, rough idle Diagnose and fix high idle or rough idle. I had the codes pulled and was told it's the idle control. I think it is lean and I've been gradually making it. The literature indicates a vac reading is normal in the range of 16- 21 inches. Functional description for the Positive Crankcase Ventilation valve, late 60's to early 70's vintage from BMC (not original equipment on the MGA): From top down the parts are assembly clip, metal cover plate, large rubber diaphragm, small metal poppet valve, compression spring, and valve body. I mean does it run real rough at idle because it should barely be running with that kind of vacuum. A couple questions: 1. To my surprise that fixed my idle so I want to say thank you for the positive information. Im around 20-24 in HG. We are at a complete loss. The note there will NOT be read. Regardless of everything else 1500rev idle is way too high. Not to be rude, but please read the whole thread before answering, I have already done the carbcleaner test and there is no leak. ) or other parts that could cause a high idle using the E30. It could be a cracked PCV hose, cracked air flow meter rubber cover, cracked vacuum line, cracked hoses to and from the aux air value, old injector O-ring seals, or a dipstick not sealing well. Just wanted to confirm the vacuum pressure at idle. Pressure readings should be taken at normal engine operating temperature, directly from the intake manifold. Soon after leaving the mechanic, I noticed my vacuum pressure gauge was reporting high vacuum pressure on idle - 5 inches of vacuum pressure on idle. Found lots of good. 2020 C8 CORVETTE on the DYNO! WAY higher horsepower and torque than GM is reporting!! - Duration: 13:35. Some resources I. I want a Radical Sounding Cam, What Should I Run? Well, this is a big issue and a LOT needs to be considered. Skewed rail pressure readings will usually not cause a hard start. Charging circuit-14V at idle. Any idea what could cause this? Vacuum leak? Dropping it so an actual tech can look at it next week. The vacuum reserve system and the. The vacuum gauge should read between 51 - 74 kPa (15 - 22 in-Hg) depending upon the. Find the cheap SUPOW Christmas Projector Light Christmas Decoration Projector LED Light 16 Switchable Patterns IR Remote Control Waterproof Outdoor Indoor Spotlight Night Light For Christmas Holiday Theme Party are perfect for adding character for your room. The idle fluctuates between 1500 and 2000 RPM's. BMW E30 3 Series Idle Speed Troubleshooting. DIAGNOSE - ENGINE IDLES TOO HIGH. once i put it in reverse it dies. -Hg, but some may produce only 15 to 17 inches at idle. If you have an automatic transmission, take the vacuum reading at idle in "Drive" (with the emergency brake on and the wheels blocked) and chose the power valve 1-2 inches below that figure. I have had a few E21 BMWs. Low compression readings would show any leak through piston/valves (although 115 to 105 is a bit of variance, but not catastrophic). I want a Radical Sounding Cam, What Should I Run? Well, this is a big issue and a LOT needs to be considered. my zx2 is starting it will idle for a few seconds then starts to idle rough. ive replaced the maf and iac sensors. i did notice that the spark plug closest to the driver was. Then I tried somethingI turned the idle mixture screws all that way closed (clockwise) to "lightly seated". I got the following codes P0171, P0507 and P2279. Sounds like a vacuum leak; revving higher with the choke on also points to that. normal vacuum for alh motor / low boost and rough idle My car always used to sit around 0. Regardless of everything else 1500rev idle is way too high. This may be the most boring thing I have ever written. More than 20% idle time is excessive. Vacuum leaks add too much air to the mixture causing the engine to run lean. The cpu usually vents the CC only during cruise conditions, and closes the solenoid at idle and WOT. A low count or percentage indicates a throttle screw set excessively high or a vacuum leak. 2nd Gen Ram Tech - High Idle After New IAC Valve + TPS - My 1999 Dodge Ram 1500 v6 has been idling very high. Read the Forum Help. After all of the idle mixture screws have been adjusted, you can finally adjust the curb idle speed screw so that the motor revs at the proper idle RPMs. We’ve seen this. I'm betting either a bad MAP sensor or the wrong part altogether. The idle is high until the engine is warm. Bleed the low side till you attain the above. 4 Idle Speed The idle rpm was recorded to determine the magnitude of the leakage compared to the idle rpm in 4. If the computerized engine control system is faulty, high idling can be one symptom. As far as the low vacuum reading goes it could be as simple as the timing being slightly retarded or the distributor vacuum advance not working properly. I think my engine vacuum is too high. BMW E30 3 Series Idle Speed Troubleshooting. I am at 3200 feet above sea level. If your engine is barely able to sustain 2"Hg vacuum at idle, it will be hard to tune using this method, but it is still useful. Engine starts, then races for a few seconds and then dies. i thought IAC was messing up. Regardless of everything else 1500rev idle is way too high. Abnormally high rpm at idle can indicate a vacuum leak somewhere between the throttle and manifold, usually pointing to cracked hoses, base plates leaks, manifold leaks, faulty carburetor or defective ported vacuum-operated switching valves. High idle remained. Read about Carburetor tuning tips including power valves and centrifugal blowers, only at Chevy High Performance Magazine. when i manually opened the throttle and then eased it closed, i noticed it would stay slightly open , but if i let it slam closed it was fine. According to the Emission Test my vehicle has a high NOx and if i performed my test correctly it seems the O2 Sensor is reading LEAN. It must also be remembered that vacuum leaks and/or poor compression can result in a low vacuum reading. built to LT1 specs with comp cam 280H,. P0506 AUDI Meaning The Engine Control Module controls the engine idle speed to a specified level through the fine adjustment of the air, which is let into the intake manifold, by operating the electric throttle control actuator. It has only crept up real high on me once during a ride. If the injectors have excessive carbon on the nozzle tip then balance rates should be high on that cylinder. This reading was 17. One way to improve our situation is to back out the adjustment on the vacuum canister slightly to lower the high vacuum value for maximum advance. When people talk about how much vacuum they have at idle, does the rpm you idle at matter ? I always read about how a big cam will give you lower vacuum numbers at idle. In conjunction with the idle jet there is an idle jet air screw. 0's and doesn't seem to affect the heat. ) The MAP sensor's probably located by the firewall on the vehicle's right side (passenger side). 5:1 and 14:1. 0 in/hg of vacuum, a 6. 5" HG at idle. The purpose of an idle air control valve is to manage the air that is bypassed around the throttle body, when the throttle plate is completely closed (idle). Power Valve Tuning: Once you have the idle speed and mixture set, take note of the Vacuum reading using your LM-1 and LogWorks software. Vacuum stayed fairly steady when idle did the same. The idle is now down to 870 RPMs but it's still not at 750 like it should be. High idle in Park/Neutral, low idle in Drive I had to set the curb idle high so that when it went into gear it wouldn't stall out. It'll probably work out as you're fooling with everything else including the tapping. The STFT stays close to zero. At cold idle it reads ~15"hg, or about -7psi. An eratic vacuum reading at idle is indicative with a vacuum leak, and can be seen with worn valve guides, but I'm not thinking that's your issue. I find it strange that it stops the problem 5 minutes before I change the pcv valve. At wot it is around 98 and hard decel low30 and high 20s at idle @ 850 rpms it sits between 45 and 50 kpa is this normal? I have no vacuum leaks all gaskets have been changed and idle is steady but if I tap the gas the revs hang for a bit. We've put together this quick-guide to reading your vacuum gauge to help you identify potential mechanical or tuning issues more quickly. i have 7 in vacuum at idle but when i put it in gear it drops to 2-3 in. gauge reading low (15-20 in Hg) but steady indicates late ignition or valve timing, low compression, stuck throttle valve, leaking carburetor or manifold gasket. If you can't get the reading into the "normal" zone by adjusting the distributor then valve timing is the problem. Your best analysis based on vacuum readings will come from your own experience, however. "It's a very common problem that results in low manifold vacuum, a. This is not a huge problem with this engine, and the idle quality is still much better than it was since now it will idle and not stall at odd times, like when sitting at a street light. Air leaking ,into, your car—not out of it—can be a problem. txt) or read online for free. HorsePower Obsessed 122,586 views. It’ll probably work out as you’re fooling with everything else including the tapping. I got the following codes P0171, P0507 and P2279. Help with High Idle Hell? Can someone please help me w/ my High Idle Hell? 1986 560SL US specs with 117,000 miles. If the motor runs better in open loop, that would indicate some type of sensor issue or. I have a VDO analog vacuum/boost gauge plumbed from my manifold. When i open the throttle, the reading DROPS (for example at 2500 RPM it shows around 260. Push and buttons until moving mark is aligned with the stationary “0” degree mark. 4 in/hg on cold starts at idle and it will stay that way till i drive for a bit then it stays at around 0. For slide-only carburetors with the slide adjustment on the side of the carburetor, adjust that. Got timing set to 32* total. This may be the most boring thing I have ever written. What's happening is the car is running pig rich at idle and part. Thanks spiffy actually its pretty weird but i was reading up on the chiltons manual and I was just stumped and couldn't figure out this problem thats been bugging me for awhile i never wanted to take it to a mechanic and have me pay them a few hundred to tell me that its something simple so I turned my air conditioner on and bam it worked lol. 0 automatic Xterra's to idle high when cold. A stock engine with worn piston rings will have a slightly lower vacuum reading at idle, plus the vacuum will not get as high on deceleration as in a healthy engine. 08 Silverado 5. 474 purple shaft/ Holley 600 DP/ stock distributor Trying to get the 383 in my new Dart tuned right. BTW, i am boosting 8lbs on the stock T25. He is an HPTuners member on this site. See if the car will run and see if that af # comes down. Or it might be spark plugs, overworking the distributor & coils. Manifold Pressure Sucks! First appeared March 21, 1999, www. does it have any thing to do with the wga? where exactly do i check. When i open the throttle, the reading DROPS (for example at 2500 RPM it shows around 260. I have a 2006 VW Jetta and the RPM is running very high at idle (neutral). With ported vacuum source at idle, vacuum is low (little vacuum advance at idle) and as the throttle plates are opened and engine vacuum increases, vacuum advance increases, which is what you want. -Connect Timing Light (SEE DRAWING No. A high, steady vacuum reading is the sign of a healthy engine. Just curious, I have a 99 aeb 1. Off-throttle coast-down will reach as high as 20"hg (which is limited by the vacuum limiter, big ugly cadmium plated diaphragm on left side of throttle body). Continue reading to find out what can cause your Civic to have idling problems. Next, hold engine speed steady at about 2500 rpm for 15 seconds and read the gauge. I just had the CEL come on for the first time the other day. I looked at my vacuum lines and I also looked at my photos from when it was apart. It all depends if it's efi or carb. The idle of a car engine is kind of like a human heartbeat: You can tell what shape it's in just by listening. Erratic rough hunting fluctuating idle vacuum leak. I have been experiencing a shudder at idle, rough shifting, sluggish power, and abnormally low gas mileage. Was this at closed throttle? If so your ITB's are way out of balance to get an idle that high. I have an Actron Scanner and have been monitoring the data. The underlying problem was the distributor. Check and set the. Any vacuum reading, whether measured mechanically or electronically, should remain steady at idle and represent a typical value for the engine configuration and operating altitude. I connected the pump to a source of manifold vacuum, and got a reading at idle. (PV) gospel: It should open below half the idle vacuum reading. PCV Vacuum I had just replaced both head gaskets and once it was all put back together I also had a problem with high idle. At cold idle it reads ~15"hg, or about -7psi. Bad Spark Plugs. Unlike a ported vacuum source (B), manifold vacuum should be high at idle and decrease off idle. An engine has higher vacuum when it is operating under light load. 25a), engine vacuum will be high. -Hg, but some may produce only 15 to 17 inches at idle. In general, subtract one inch for each 1000 feet above sea level. Tahoe & Suburban - I cleaned my TB now high revs @ idle - 2007 5. The reason the vacuum increases with RPM, is because the momentum of the air overcomes the effect of cam overlap. ) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more. Thanks spiffy actually its pretty weird but i was reading up on the chiltons manual and I was just stumped and couldn't figure out this problem thats been bugging me for awhile i never wanted to take it to a mechanic and have me pay them a few hundred to tell me that its something simple so I turned my air conditioner on and bam it worked lol. PHOTO 9 Engine vacuum readings should be steady and increase as the rpm is raised from just off idle to approximately 2,500 rpm; if not, the exhaust is restricted. 1995 Dodge Ram 2500 Failed High HC Only at Idle. I connected it to an ELM327 clone adapter. If not , could you possibly have a vacuum leak or a cable pulled ? Just throwing out some initial thoughts. Questions to ask yourself! i. Hg of vacuum at idle. I want to say it should read more like 3-4 @ idle. Adjusted mixture screws by idle speed as the vacuum did not change. Temperature seems to affect boost on pcm control because it's torque based. The engine may run well at higher RPMs, but surges, runs rough and struggles to maintain stable RPMs at idle. Checked vacuum on the PMS display. Try to achieve an acceptable idle speed while maximizing Vacuum and getting Air/Fuel Ratio between 12. 0's and doesn't seem to affect the heat. At distributor, leave vacuum line disconnected and plugged. 5 power valve might not be right for you anymore Fatten up your idle mixture so it is a bit richer than usual. Although the amount of vacuum will vary by application, most will register between 15 inHg and 20 inHg (50 kPa and 70 kPa) at idle. BMW E30 3 Series Idle Speed Troubleshooting. Next, check for vacuum leaks. If you have an engine at idle and your vacuum gauge reads very low, or no vacuum, you are probably connected to ported vacuum. Soon after leaving the mechanic, I noticed my vacuum pressure gauge was reporting high vacuum pressure on idle - 5 inches of vacuum pressure on idle. Q: I am banking on you solving this problem. 3 high idle issue. How to Properly Set You Mustang's Idle. Problems with idle speed—things like slow idle, fast idle, rough idle, or stalling after idling for a few seconds—are symptoms that something is wrong with your engine. Found lots of good. Needle moves slowly through a wide range of readings. With the engine running at idle, transmission in park or neutral (emergency brake set), take a reading of the gauge. He is an HPTuners member on this site. 0 in/hg of vacuum under engine idle vacuum. If you're at altitude, these readings may be lower (supposedly by 1 inch of mercury for each 1000ft above sea level, roughly). Check around your intake for leaks, and for any hoses that might be loose or disconnected. I advanced the timing to 12 degrees, readjusted the idle mixture screws and now I have about 13-14 inches of vacuum with the idle set at 650 rpm. ive replaced the maf and iac sensors. How the PCV VALVE Works - CV-103. Mine is high so does spraying the brake cleaner bring idle down or raise it further?. 5 power valve would be a good first selection. I don't really understand why the LTFT is very negative, because the O2 sensor reading is normal and based on that the LTFT should stay close to zero. So this means my engine running at a very high idle is not from the bad MAP Sensor? I have two Vacuum hoses that come over and T off, plugging into the Throttle Body (one plugs in above the other so. When you snap the throttle, the manifold vacuum drops, so the absolute air pressure going into the cylinder increases. Exhaust Back Pressure Starting with the engine at idle, slowly increase engine speed to 3,000 RPM. 1 Welcome, Guest. MB M110 Engine Vacuum Connects - Free download as PDF File (. Running rough & high idle---found culprit?? After all the feddback and more reading, I am thinking vacuum leak but have not yet had time to diagnose it. Excessive idle time can cause white smoke when cold due to carbon build up on injector tips. gauge which verifies the low vacuum. Next, check for vacuum leaks. I have an Actron Scanner and have been monitoring the data. The MAF and MAP sensor readings are low for my area sea level. Charging circuit-14V at idle. The vacuum gauge should read between 51 - 74 kPa (15 - 22 in-Hg) depending upon the. Next, check for vacuum leaks. I take ABSOLUTELY ZERO CREDIT for the length of material you're about to read, however I have made a few comments in-text that you can see which I will highlight in green. Wait, did you replace as a warranty claim, or did you have access to a known good unit? You need your idle vacuum reading to assess this more accurately, but my guess is that there’s a severe leak outside of the FI unit’s domain. SYMPTOM SUMMARY The engine idles too high. When warm, still misfires, but I’ll sometimes get a high RPM in Park, especially with a hot engine. The idle jet controls the idle and on up to quarter throttle, give or take a bit. With the engine up to operating temperature (readings will vary depending on engine temperature) and idling, connect the vacuum gauge to the port and note the reading. gauge which verifies the low vacuum. i am pretty sure it was more like 12 to 15 just last week. Erratic rough hunting fluctuating idle vacuum leak. MB M110 Engine Vacuum Connects - Free download as PDF File (. The engine may run well at higher RPMs, but surges, runs rough and struggles to maintain stable RPMs at idle. Idle Vacuum What is Idle Vacuum? Idle Vacuum is the intake manifold vacuum when the engine is idling. 0193 kPa (1 in-Hg) FROM THE SPECIFIED READING FOR EVERY 304. The only way to get it to stop it to come to a complete stop and pull in the clutch and it will go back down to the normal idle. When you have adjustment sensitivity on the idle mixture screws, you can then balance the idle mixture. gauge reading steady but dropping regularly indicates burnt valve or improper valve clearance. Hall explains how a pump functions to produce vacuum and how someone can get a better reading on how much vacuum their engine is producing. The most common symptoms of a vacuum leak are rough/high idle, misfires and a check engine light. Holley Carburetor: Idle and Transition Circuit Calibration Guide July 27, 2015 by Muscle Car DiY At the risk of sounding repetitive, let me say once again, that if you bought an application-specific carb, you probably are only going to need to do minimal adjustments to mixture calibration. The idle of a car engine is kind of like a human heartbeat: You can tell what shape it's in just by listening. 2001 F-250 high idle after start (5. At distributor, leave vacuum line disconnected and plugged. this current is picked up by the sensor and tells the welder to go to high idle. Don't know if the hard starting is related, but I assume it is. Turn them out to richen the mixture. 3 Felxfuel I cleaned my throttle body, now I have high RPM at idle around 2000. ) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more. A massive vacuum leak can cause the car rev that high. A high count/percentage indicates an overly closed throttle plate screw setting or an air intake obstruction (clogged air filter or throttle body). One way to improve our situation is to back out the adjustment on the vacuum canister slightly to lower the high vacuum value for maximum advance. 20in is pretty normal. I don't have any check engine lights as of yet, but I don't know what is going on with the idle. 480 lift, 230 degrees duration @. If the IAC number has not increased, then review the article above regarding high idle from a vacuum leak or high idle from sticking linkage. This is compounded if the mixer is over sized for the engine. An eratic vacuum reading at idle is indicative with a vacuum leak, and can be seen with worn valve guides, but I'm not thinking that's your issue. Is it possible that the idle is high because the ECU is not used to reading the increased airflow? A ton of black stuff came out of it while I was cleaning it. I cleaned the idle air control valve and the problem was fixed again. Gauge needle drifts slowly over a range of 4 to 5 in. Read about Carburetor tuning tips including power valves and centrifugal blowers, only at Chevy High Performance Magazine. Is the idle steady or does it fluctuate? Is it just the idle that is rough or does it continue up the RPM range? If it smooths out what RPM?. Then shut the car off, and plug the idle screw back in, start car, done. Then retard the timing until the vacuum gauge reading drops slightly, approximately one half to one inch. First step was going to make sure idle circuits were tuned then go from there with the power valve and maybe larger pumps. If the reading is low, check to see if the vacuum hose is kinked, clogged or cracked. ) The MAP sensor's probably located by the firewall on the vehicle's right side (passenger side). Intake is Edelbrock Air Gap with Holley 600 dual line. eased idle speed back down to 900-950, did the same test as earlier, putting car in gear with foot on brake - engine stalled out almost immediately. The answer will divide the possible sources of additional air into two, greatly simplifying the problem. You may also find a P0300 "random misfire" code. If the engine has a high performance cam then vacuum will be alot lower. If you are experiencing a rough idle or your RPM is running high, then there are a variety of reasons for why this could be happening. 5 rated power valve. Mine is reading about 16, but the needle is bouncing back and forth very rapidly 4-5 hg either direction constantly at idle. And also that it keeps getting worse. At idle, more ignition timing means more manifold vacuum, at least up to a certain point. When you snap the throttle, the manifold vacuum drops, so the absolute air pressure going into the cylinder increases. Cruise Calibrations. With the vacuum advance connected, it looks like I have about 25-30 degrees of total vacuum at idle. I just wanted to share it with you. Don't know if the hard starting is related, but I assume it is. My only guess is the flywheel being so light requiring More air to idle _____. If you have a carb that uses a "power valve" to enrich the mixture under load. First step was going to make sure idle circuits were tuned then go from there with the power valve and maybe larger pumps. Vacuum leaks. Audi 5000 / 200 / V8 Discussion - high Idle - Ok I have hit a wall, and now looking for help amongst the experts here. i think i have a vacuum leak. if i put it in drive it ill really rough and drives to pull itself it will bounce between 1500 and 2100. First start and check if the choke is not adjusted properly. An idle system will have an idle jet/restriction that must be changed to supply the desired fuel mixture for idle and off idle engine demands. I had various idle problems on my 300E, I am pretty sure it was due the very degraded wire harness on top of the engine, but I traded it before digging into it any further (rest of the car was not that great either). The high idle is often caused by a vacuum leak but I'd probably guess your IAC (idle air control) is dirty and hanging up letting too much air into the throttle body. The problem is; "race cars" that have those nasty sounding cams are completely different than cars that are driven on the street. the low vacuum is not pulling the step up spring down to seal off the. Hi, I'am having a problem diagnosing a 1979 40 hp mercury I bought for my whaler to repalce a blown 35 Evinrude. The high idle sounds like a vacuum leak, but I have yet to find it. Run the engine at idle, low cruise (1800 to 2200 rpm) and high cruise (2500 to 3000 rpm). no more low / high idle. any thoughts? _____. My local baro pressure is 29. This makes it so much more easy to do fault finding or doing repairs. 5 rated power valve. The high RPM contributing to a steady vacuum reading is only masking the problem. It seems slightly down on power and mpgs. Replaced all the vacuum lines. Below are the top 5 causes that a mechanic would look for. 8t, no intake mod's other than K&N filter in stock air box. Vacuum gauges are among the mechanic's most useful but lesser known tools. If the engine you are working on is equipped with a power valve (no metering rods), the main jet size is what determines the A/F mixture that will be delivered to the engine at light-load/cruise speeds. 5 power valve would be a good first selection. High idle in Park/Neutral, low idle in Drive I had to set the curb idle high so that when it went into gear it wouldn't stall out. 35 low 150 high at 1500rpm. Next, hold engine speed steady at about 2500 rpm for 15 seconds and read the gauge. 75 and at WOT it read 4. 20 in gear at idle. A helpful hint: All of the vacuum readings on the vacuum gauge should be the same for each screw you adjust. • At medium throttle opening, when cruising (Figure 3. We let it idle for about 10 minutes then like clockwork, the idle rpm picked up to about 1200 and the ESS warning light illuminated. 0 out all enrichments. Returned a suspect IAC today and he mentioned MAP sensor? Might be time to spring for a new MAP even though I've get no codes.