re: continued troubleshooting posted here : http://forums.bimmerforums.com/forum/showthread.php?t=363771

Checked the Motronics, zero resistance on 47, 48 (reference sensor, should be 540 ohms), zero resistance on 4, 22 (idle air stabilizer valve, should be 40 ohms), resistance on 7, 12 (air flow sensor) but does not fluctuate when starter actuated (it should).

The cars starts, runs rough. Plugs are heavily carboned, other symptoms in referenced thread. I changed the timing belt about six weeks ago, it was running fine.

The car passed the Motronics throttle test: 1444

Yes, mulitmeter is functioning properly :)

Could the Motronics unit be bad..partially bad but still show 1444 and the car run?

One week of troubleshooting, verrrrrry frustrated with my lil car.

1990 325i

Thanks for any help.

Jim

Ignoring the resistance readings on the reference sensor and idle air valve for the moment, check to see if the flap in the air flow meter is stuck open or binding.

*nod* It has a full free range of motion..

There's no mention of the "check engine" light being on, so I'll assume it's not. That indicates a fault in a component not monitored by the DME. So, time to check fuel pressure.

Solution found:

The reference sensor wires had chafed, grounding it out. As for the motronic, that was an ID ten T error. :rolleyes

Wait, I mean don't ignore the resistance readings!

I would think a shorted sensor would log a fault in the DME. Lacking that, and with multiple components seemingly showing short circuits, it seemed logical to look elsewhere first. Good job finding the fault. But what's up with the idle air valve?

The flap has full range of motion. The umm *coughs* resistance readings were caused by my own ignorance. Although, the air sensor resistance does not vary when the starter is engaged, as the book says it should.

Runs fine now, although idling rough and occassionally not hold idle and dying off. But I'm reserving judgement on that until I get my new copper plugs from bavauto this week. The current ones are severely carboned...

On the bright side, just as I've seen mentioned in these forums, I learned a TON about my bimmer by doing all this troubleshooting myself. A got a few new parts put in, which is never a bad thing.

Correct me if i'm wrong but once a plug is fuel fouled it cannot be cleaned up by driving, even once symptom is fixed. You mentioned it was carbon fouled but if it was running very rich or was flooded at one time I believe the plugs are toast. They will work but the motor will run rough. If everything was fine before the belt change is there a chance it slipped a cog?

I'm only running on the old plugs until tomorrow/next day. Couldn't find the Bosch coppers in this town, and ya wouldn't have me sticking platinums in there riiiight? :)

The problem was an infrequently grounded reference sensor. Runs smooth now other than at idle.

Ignoring the resistance readings on the reference sensor and idle air valve for the moment, check to see if the flap in the air flow meter is stuck open or binding.
why do you ignor resistance readings? I have reading all over the place and car runs rich. shouldnt the readings be increasing as the valve opens?

I don't ignore my own readings. I suggested that Jburkman ignore his for the time being, because zero resistance in multiple components suggests errors in testing. I also suggested several basic checks consistent with his car's symptoms, which also apply to your situation.

There is no direct resistance test for flapper-type air flow meters. Proper testing requires the use of an oscilloscope. If your car is running rich, check the flap for proper operation, then check fuel pressure.