Does E30 have a "Safe Mode"? Could this be a Crank Position Sensor?

[95BMWIC]

I had a weird issue that happened this morning - I'm at the office and haven't had time to diagnose - so i thought Id reach out to anyone that has had a similar issue.

My 91 BMW suddenly loss power yesterday on the way to work - loss idle, died, started, drove but stumbled at idle for a 1/2 mile or so. I pulled into a parking lot and then it started idling fine. Went to work (a couple of hours) Stared and drove 30 miles home with no issue.

This morning - started car and let it idle for 10 minutes, idled fine - begin to drive and the car stumbled when leaving driveway. It ran poorly (stumbling idle) -and then experienced a total loss of power. Car would not go above 1500 RPMs - and would not rev - so put foot on gas to keep car moving around the block, but RPMs stayed constant and the car pulled itself around the block at 1500..

Pulled back into driveway -car was idling - parked in the garage.


Any thoughts on this condition?

Does the E30 have a "Safe Mode"?

I don't have my Bentley here at work - but I wonder if the Crank Position sensor could be bad? Does a bad Crank sensor cause this type of issues?


NO Codes. Vacuum is pulling at 16 (normal) no problems with hoses, or boots. I recently changed the timing belt (500 miles ago) - so maybe disturbed the wiring on CPS?

[dnguyen1963]

I have had this happened to me once a long time ago. When I tried to start the car at -5F, I had trouble starting. The car finally started, but the idle was rough. I could not rev above 1500 rpm and could not drive above 20 mph. Once the temp warmed up to 15F, I disconnected the negative battery cable to reset the ECU and then could drive the car normally.

[95BMWIC]

I have had this happened to me once a long time ago. When I tried to start the car at -5F, I had trouble starting. The car finally started, but the idle was rough. I could not rev above 1500 rpm and could not drive above 20 mph. Once the temp warmed up to 15F, I disconnected the negative battery cable to reset the ECU and then could drive the car normally.

It was cold here but I had it plugged in (oil pad heater) and it temp gauge was warm... I will reset tonight.

Any idea what caused your issue? Or did it correct itself after that?

[superj]

What engine do you have?

I had a 325i that did the same thing and it was caused by the crank sensor having a bad connection at the sensor end. When I hit a bump a particular way, it would lose half of the cylinders and barely run. Than, when I hit a bump a certain way again, it would go back to normal.

I found it by starting the car and wiggling wires in the engine bay.

[TobyB]

nope, no limp mode... It's stiff all the time. Until it falls off...

fuel supply, I'd add to crank sensor.

t

[95BMWIC]

What engine do you have?

I had a 325i that did the same thing and it was caused by the crank sensor having a bad connection at the sensor end. When I hit a bump a particular way, it would lose half of the cylinders and barely run. Than, when I hit a bump a certain way again, it would go back to normal.

I found it by starting the car and wiggling wires in the engine bay.

Engine is the M20 - 1991 stock with Auto transmission

Ok - I will check that - I remember having to disconnect the CPS from the bracket and route the wire around a fuel hose when doing the timing belt change.

[95BMWIC]

nope, no limp mode... It's stiff all the time. Until it falls off...

fuel supply, I'd add to crank sensor.

t

fuel supply - good point - I will swap fuel filter - and check fuel pressure.

[nando]

There's no limp mode for a bad CPS. The CPS is actually the only sensor the M20 absolutely cannot run without. Everything else has a fallback.

[dnguyen1963]

It was cold here but I had it plugged in (oil pad heater) and it temp gauge was warm... I will reset tonight.

Any idea what caused your issue? Or did it correct itself after that?

Yes, once I reset the ECU it was running fine.

[95BMWIC]

Update

Before checking fuel pressure (went to HF and bought a cheap gauge) I decided to run the car -make sure it is running like crap - and unplugged the AFM..

https://youtu.be/f1iaL5YhmTU

Assuming this may be the issue? Either that or somethings really a miss..

Will report back after an AFM swap.

[superj]

I won't be of help. its hard to watch videos at work and I forget to check when I get home

[95BMWIC]

Swapped out a good AFM - started and idled fine.. seems like its back to normal after driving 70 miles.

I think that's the issue.. however -

I'm not completely convinced - it could be intermittent - I will update again if it begins to run bad..

[superj]

Ok

[dnguyen1963]

Swapped out a good AFM - started and idled fine.. seems like its back to normal after driving 70 miles.

I think that's the issue.. however -

I'm not completely convinced - it could be intermittent - I will update again if it begins to run bad..

One more thing that I forgot to mention. When it was that cold, my AFM had many ice crystals built up inside preventing the flap from operating correctly and that screwed up the idle.

[ForcedFirebird]

Swapped out a good AFM - started and idled fine.. seems like its back to normal after driving 70 miles.

I think that's the issue.. however -

I'm not completely convinced - it could be intermittent - I will update again if it begins to run bad..

There's no limp mode for a bad CPS. The CPS is actually the only sensor the M20 absolutely cannot run without. Everything else has a fallback.

The m20 will only idle if the AFM is bad or unplugged, it's not like a later cars with a MAF that has some sort of "default" if it's absent. Simple test, go outside, unplug the AFM and see if the problem replicated (I am pretty confident it will be). If it is, plug the AFM back in, and go home knowing you fixed the issue. :)