M20 Running

[87bimmerguy]

edit: thread title should be "M20 Running Like Crap"

Yes, I searched.

This problem just appeared overnight about a week ago, it didn't happen gradually.
When cold, the car starts right up and runs great. As the engine warms up, it runs rougher and rougher and once it's up to normal temp it runs like crap, like it's missing a cylinder or two. However this is only under load (accelerating), and only when hot. Once I'm up to speed, if I let up on the accelerator the engine smooths out and runs like normal. If I give it more gas it runs horrible again.
I suspected a vacuum leak, but I've checked the main areas and can't find anything.
Any ideas?

BTW I did the timing belt a couple months ago, and at the same time replaced the spark plugs, distributor cap and rotor, cam seal, water pump, and did a valve adjustment.

Thanks,
I'm tired of it sounding like a lawnmower.

[87bimmerguy]

Bump need some help guys, Thanks

[Sir Smirnoff]

probably the o2 sensor. How many miles on the car and is it original? Check some of my previous threads for o2 sensor rants. It seems to be a common issue with old e30's

[87bimmerguy]

Yeah I thought about that too, but I replaced it about two years ago, which would put it around 25,000 miles. I guess it could be bad, I could always disconnect it and see if it goes away.

[87bimmerguy]

Well I just disconnected the o2 and drove the car, didn't make any difference. Any other ideas?

[jlevie]

These symptoms don't sound like they would be caused by a bad O2 sensor. The sensor might need to be replaced as the useful life of an O2 sensor is not more than 100k, but something else is causing the rough running under acceleration. The most credible causes would a fuel delivery problem or a bad AFM.

[87bimmerguy]

I was wondering about the possibility of a fuel problem. How do I go about testing the FPR or AFM?

[jlevie]

The Bentley manual has a suite of tests for the fuel system. The simple test for the AFM is to see if its resistance varies smoothly with vane angle. But the best test is to swap in a known good AFM.