The more I drive it, the worse it runs

[Beej '86 325es]

Lately, I will drive the car, and after about 30 minutes, I've noticed it runs slightly leaner at WOT. Then, the next time I cold start the car it idles like crap, and it gets worse each time I cold start it or run at WOT.

However, if I disconnect the DME for 30 seconds, voila! It runs great again. I've got two DMEs that I go back and forth with using the same chip and have the same results. Is it possible I have two bad DMEs?

[jekaio]

check for vacuum leak.

[evandael]

long term vs. short term O2 sensor fuel trims? the DME may not be getting the proper reading from the O2 sensor under WOT to adjust the fueling needs.

as far as the cold starts.. maybe the O2 sensor heater isn't working and the DME is not sending enough fuel due to the improper reading. the issue may get successively worse as the ecu 'learns' with each successive drive; maybe that's why it's remedied for the short term when you disconnect and reset them.

try the O2 sensor heater 12v backfeed fix, check plugs and O2 sensor, let us know!

[MaxBell]

LOL I have a very similar problem.

I thought TPS sensor, if the car doesn't know how much throttle you're giving.
I also thought, more successfully, that it was the MAF. I gave mine a clean with MAF sensor cleaner and the problem has gone away.

Turning the car off and one with make the problem go away for me, though it would happen more often.

I'll be looking to replace the MAF in the next few days.

[Beej '86 325es]

long term vs. short term O2 sensor fuel trims? the DME may not be getting the proper reading from the O2 sensor under WOT to adjust the fueling needs.

as far as the cold starts.. maybe the O2 sensor heater isn't working and the DME is not sending enough fuel due to the improper reading. the issue may get successively worse as the ecu 'learns' with each successive drive; maybe that's why it's remedied for the short term when you disconnect and reset them.

try the O2 sensor heater 12v backfeed fix, check plugs and O2 sensor, let us know!

I thought it was like the long term/short term fuel trims working backwards. But for cold starts and WOT at the top end, those should be pre-programmed and do not take input from the O2 sensor. So it does not make sense to me why they would change.

I've done the O2 backfeed mod and just changed the plugs 100 miles ago.

I think I'm going to take it into one of the local BMW shops. I've got a code reader (it's not throwing any codes), but I think if someone who knows the engine had a scan tool that could monitor the operating parameters, they might be able to figure it out.

[nando]

because the long term trim affects WOT and cold starts. they don't use closed loop but that doesn't mean that O2 feedback doesn't apply.