Hesitation and rough running - still

[Kurt S]

Well hello, it's time once again for me to play find the gremlin. To recap, my 87 Carrera likes to cough and buck and sometimes backfire slightly when cold but these symptoms mostly go away when it's warmed up fully. However, after it's warmed up, a new malady rears its ugly head. That being, if I'm coasting down hill or decelerating with my foot off the gas, when I step on the accelerator again it's like the engine was shut off or is out of fuel. Nothing happens for a few seconds and then it will cough and lurch and start running again. This doesn't happen but maybe 10% of the time which makes showing a mechanic what it does almost impossible. When it does this I've pushed in the clutch instantly to see if it dies and it does not, it drops to a nice smooth idle. When cruising along at light throttle setting the engine doesn't feel smooth. It has a slight uneven feeling that could be described as running too lean or having the timing too far retarded, if that were possible with this car. I've never had trouble starting it or had trouble with a high or uneven idle.

I just replaced both the DME relay and the CHT sensor and the problem remained the same. The car has 55,000 miles and had a major tune and service done last year at 50,000 miles. At the suggestion of a local shop I just put a bottle of Techron fuel treatment in it to see if it might possibly clean something out from the injectors or wherever.

The shop has offered to spend three to four hours diagnosing the problem for me (at $75 an hour) but as I'm mechanically inclined and have an ultimate set of tools the phrase, "I can fix it!" is quite meaningful to me.

Anyone have any further suggestions? Anyone? Anyone?

Thanks!

Kurt S

[scottb]

O2 sensor?

[jperry]

Check your fuel pressure and pump output.

[warment]

I had the same thing happen on my 2000 Mustang GT. Turns out I had a dirty "idle air bypass valve." The rpms would also drop very quickly between gear shifts and the car would stall at stoplights.

I cleaned the valve and everything has been fine. I don't know if your Porsche has one(I assume it does). Might be something to check out...

Bill