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Hi there. The above car suddenly surges and stalls when trying to idle. Open throttle seems okay. If I disconnect the PCV hose it idles okay. There is a lot of pressure that builds up on the valve cover hose fitting, but very little vacuum from the throttle body. Even so, when I block the hose the engine stalls immediately. I believe this car has no PCV valve, but all the passages seem clear. Thanks for any ideas.
shade tree mechanic
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moved to E36 sub forum
check the ETK with your VIN for the parts details http://bmwfans.info/
you had the same problem 2 years ago https://www.bimmerforums.com/forum/s...alling-at-idle
there were some detailed proposals what to check, but you never posted again, what you did and if that solved the problem. Better give an update what you did so far, changed, tested etc
Last edited by shogun; 03-02-2023 at 09:49 PM.
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Did you replace the AFM?
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Replaced the AFM and seemed good after that. Unlike before, the problem came on suddenly and is constant. Won't idle at all, regardless of temperature. Smoke test indicates no leaks. No codes other than the knock sensor one that it's had for years.
Member
Have you ever replaced the coils? If not they need to be done. Has the o2 sensor ever been done? Do the knock sensor at the same time, its critical for proper engine operation. Do the spark plugs at the same time.
You need to do all the maintenance items you've been forgetting.
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Use Rockauto, Bosch, NGK, NTK. Usually there is a 5% off code out there, check Retailmenot.
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It looks like your car uses HT ignition wires, if these are old they definitely need to be done. They will leak high voltage and it will loose a lot of performance. The wire set is not cheap because its not a generic set. ~$100. Be sure that the wire set says high quality silicone, years back they made them out of lower quality rubber and those would wear out faster.
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Your car uses 2 knock sensors, they both need to be done.
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You should test your crankshaft sensor, usually its 510 ohms but it may be different for your car.
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Spark plugs and wires were replaced about two years ago, less than 6000 miles on them. O2 sensor about the same. I was thinking it might be the purge valve, as you can blow right through it. When the engine is running there is 12v across the terminals, which closes it. All the info I can find says the valve is normally closed, and power opens it, but it's not supposed to be open when the engine is cold or idling. Mine is exactly opposite. Either way, clamping the hoses makes no difference. BTW, car has 4 knock sensors, one per cylinder. I will replace them all next time I remove the intake manifold, which will hopefully be never.Originally Posted by Eric93se
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M42 has 2 knock sensors and 4 ignition coils.
Don't complain about your car not running right if your not willing to pull the intake off to fix it.
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Purge valve should be closed with no power... (should not be able to blow through it)... i just did this on my M3 to try and pass smog. Replaced it with a genuine BMW part (Febi lasted less than 3k miles). The valve being open during idle could potentially cause the car it stall as well.
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The valve is closed during idle, but it's closed because the computer is supplying 12v across the terminals. In other words, it's doing what it's supposed to do, but for the wrong reason. As for the intake manifold, I've removed it twice before, and it's a nightmare. If I was convinced that one knock sensor out of four would cause a sudden stalling/surging problem when the code has been there for years, I would do it again without hesitation.
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I have an update. It's obviously running too rich, based on tailpipe fumes and intermittent dark smoke as the engine bogs down. I did a hard reset of the ECM. Tried running with the O2 sensor disconnected. Nothing has made any difference, except that if I remove the pcv hose, which admits unmetered air, it runs better. Thanks for all your suggestions so far.
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DO you have the problem that this guy has? https://www.youtube.com/watch?v=DaOCwNeFXPs
Also is your PCV still broken? Im thinking you got a vacuum leak some where
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Replaced the crankcase vent hose. Passed the smoke test. Tomorrow I plan to clean the IAC valve (again). I did it a couple of years ago along with its hoses. I could see and feel it working when I applied 9v to it, but it's the original one, so maybe it has failed this time. Thanks for not giving up on me.
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It was the air flow meter. A year and a half ago I replaced the original with a Chinese-made one in order to correct an intermittent, temperature-related stalling problem. It worked, but there were some trade-offs. So I put the original one back on, and it's running flawlessly again with the exception of the stalling problem. So apparently the Chinese one had a sudden catastrophic failure. I've been examining it to try to see what went wrong with inconclusive results so far. Strangely, the potentiometer in the Chinese one ranges from 250-600 Ohms, when I move the vane, while the original Bosch one stays on 8500 Ohms regardless of the vane position. It's a puzzle. Thanks for your help.
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Well if your measuring the Bosch one correctly then its obviously bad.
Last edited by Eric93se; 03-27-2023 at 09:50 PM.
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shade tree mechanic
Moderator
more details pls, when you measured 8500 Ohms, between pin ? and ? Some people mix it up http://www.m42club.com/forum/index.php?topic=950.0
https://www.bimmerforums.com/forum/s...ss-Air-Flow%29
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I'm measuring between pins 2 and 5 on both units. I took the Chinese one apart sufficiently to check continuity on everything, and made a schematic for myself, and determined that #5 is the ground and #2 is the wiper for the potentiometer. Although I plan to take the cover off the Bosch to see if the pins are connected the same way, I feel confident that they are.
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