Carpokes Porsche Forum

Hello Guys,
I need a little help here with diagnosis. I have a ‘91 S2 with 116K miles. It is currently exhibiting an intermittent problem that is driving me nuts. So, when cold, it always starts well, settling into a nice steady idle. However, if I drive it, when pulling away it often is hesitant to take throttle right away, acting like it’s either running way too rich or too lean (hard to tell), until it gets above 2,000 RPM at which point it seems to clear out and run just fine. Come to a stop, idles fine, pulls away fine. But if I should stop somewhere and turn off the engine and I come back fairly soon while the engine is still warm, it is often very hard to start and when it does, it cycles up and down from 500 RPM to 1000 and will not take any throttle, often stalling. It may do this several times or it may start and idle just fine. It’s that intermittent.
What do you think? It has a new fuel pump (replaced for another reason) though it did the same thing with the old one. It came with a with a new check valve. Throttle position sensor? It was replaced some years ago, when the car wouldn’t idle at all. Fuel injection damper? Fuel injection regulator? Any thoughts would be most helpful.

Me again. I fixed it. It turned out to be real simple. Under the old adage of not "overlooking the obvious" I decided to just make sure all the vacuum lines were attached to something. The very first one i checked was the line coming off the Fuel Rail Damper. It comes off the Damper and disappears under the intake manifold but I followed it and found that it wasn't attached to anything!  Right near the end of the hose was a three-pronged hose connector with a missing hose. Plugged it in there and damned if that didn't fix it. I was so happy.

Mark802 wrote: Mon Apr 28, 2025 7:58 pm Me again. I fixed it. It turned out to be real simple. Under the old adage of not "overlooking the obvious" I decided to just make sure all the vacuum lines were attached to something. The very first one i checked was the line coming off the Fuel Rail Damper. It comes off the Damper and disappears under the intake manifold but I followed it and found that it wasn't attached to anything!  Right near the end of the hose was a three-pronged hose connector with a missing hose. Plugged it in there and damned if that didn't fix it. I was so happy.

Good work! Sorry I missed this question. Checking for vacuum leaks is my Pavlovian response to most questions.