Running Issues Facelift M20B20 AUTO
Posted: Mon May 11, 2026 4:50 pm
So the last 3-4 years I've been chasing a running issue on my E30. Now it's worth mentioning that this might be one issue or a series of different issues. It all started a few years ago, with a cold engine when I put my foot on the throttle when the rev counter comes down it would struggle to idle momentarily, but not cut out just grumble for a second like it wanted to cut out. Also when I would approach traffic lights and come to a stop with the engine idling, it would sound like the the engine is hunting, but the rev counter wouldn't move.
Anyway after a summer of these symptoms, it got progressively worse and got to the stage where it would cut out when I would take my foot off the throttle and let it idle. I could not drive the car without it cutting out when coming to a stop. This was improved and made driveable by hooking the car up to an emissions machine and adjusting the AFM. I then ended up with just a grumble from the engine when the rev counter would come down to idle... and that's pretty much how it's remained. Sometimes it's better, sometimes it's worse. I do remember towards the end of last summer, it was cutting out when I was maneuvering with the car in reverse. But so far this summer it's been running well, all I've had is a bit of a lumpy idle at junctions/traffic lights.
I've thrown a number of parts at this car over the last few years to rectify this entirely but with no luck.
Smoked tested, no leaks
TPS replaced (new genuine BMW)
Idle control valve replaced (new genuine BMW)
AFM sent away to be refurbished.. no faults found with it.
Fuel pressure regulator replaced (new genuine BMW)
Car is serviced every year, so spark plugs, valve clearances all done at some stage.
ECU replaced with deadstock unused unit. EPROM swapped over.
Rotor and dizzy look fine.
HT leads fine.
All relays and fuses are okay.
My last throw at the dice is perhaps the crank position sensor. This failed on me back in 2011, and at the time I could only get ahold of a chocolate euro car parts equivalent, which has done the job but is maybe on it's way out. Not sure if these just fail or work though. No inbetween.
Other than that my only other thought is perhaps the EH autobox, and something awry there.
This seems to have baffled most BMW speacilists around.. so any help appreciated.
Anyway after a summer of these symptoms, it got progressively worse and got to the stage where it would cut out when I would take my foot off the throttle and let it idle. I could not drive the car without it cutting out when coming to a stop. This was improved and made driveable by hooking the car up to an emissions machine and adjusting the AFM. I then ended up with just a grumble from the engine when the rev counter would come down to idle... and that's pretty much how it's remained. Sometimes it's better, sometimes it's worse. I do remember towards the end of last summer, it was cutting out when I was maneuvering with the car in reverse. But so far this summer it's been running well, all I've had is a bit of a lumpy idle at junctions/traffic lights.
I've thrown a number of parts at this car over the last few years to rectify this entirely but with no luck.
Smoked tested, no leaks
TPS replaced (new genuine BMW)
Idle control valve replaced (new genuine BMW)
AFM sent away to be refurbished.. no faults found with it.
Fuel pressure regulator replaced (new genuine BMW)
Car is serviced every year, so spark plugs, valve clearances all done at some stage.
ECU replaced with deadstock unused unit. EPROM swapped over.
Rotor and dizzy look fine.
HT leads fine.
All relays and fuses are okay.
My last throw at the dice is perhaps the crank position sensor. This failed on me back in 2011, and at the time I could only get ahold of a chocolate euro car parts equivalent, which has done the job but is maybe on it's way out. Not sure if these just fail or work though. No inbetween.
Other than that my only other thought is perhaps the EH autobox, and something awry there.
This seems to have baffled most BMW speacilists around.. so any help appreciated.