If it’s not the ISV, it could be.....
 

My new to me 1992 964 has a cold idle issue. It will stumble and stall, stumble and stall. The ISV is brand new. Plugs, wires, rotor, cap etc all new.

Any ideas what else could be causing this issue?

Love the car but the cold starts are killing me.

Thanks
Chris

Hey Chris, have you checked the idle microswitch? Easy check. In a quite environment, with the engine Off, push the throttle open slightly. You will hear the switch's contacts open and close as the throttle is opened/closed. The throttle only has to move a millimeter or two from it's idle/home position to hear the contact open/close. It's kind of a tick or click sound. Google idle microswitch to see what it looks like. Good luck.

Thanks John.

I’ve been reading a bunch of older threads and making a list of potential candidates.

Anyone have experience with the DME relay?

I also find the accelerator to be more “on/off” than my 81 SC so I wonder if that could be ‘tied to this?

Thanks again for the suggestion.

Chris

i have a '92 C2 which had the same problem that you're describing. in my case it was because the cylinder head temperature sensor had failed.

Thanks Deckard.

Prior to replacing the sensor, did your call continuously stall at start-up until the car reached proper operating termperature?

After it is warm, the car drives perfectly and idles at stoplights etc with no issue.

Thanks,
Chris

yes it did. until it warmed up the engine would flood. when it would stall after the first start, when the engine was cold, i had to restart it with the gas pedal all the way to the floor. i would have to do that a few times each morning. when it was warm it ran just fine.

just to add. it would start up immediately for the first start of the day. it would run ok for about 1 minute then the problems would show up with all the symptoms of flooding.

Based on what I've read and the feedback received, I have compiled the below list. Any other suggestions? As mentioned, the car stalls at start-up and continues to stall out until warm. Please feel free to let me know if any of the below should be removed given that it eventually warms up, idles and drives normally.

1. O2 sensor?
2. ISV properly installed? Backwards?
3. DME relay
4. Engine Temperature Sensor
5. Vacuum leak?
6. Idle microswitch set-up / throttle linkage
7. Cylinder head temperature sensor

Thanks,
Chris

Have you done an idle adaptation with the hammer?

That list is good. Check your battery as well and if you haven’t swapped your coils they could also be the issue.

So, we’re chunking through the list and still no resolution.

Uwanna, unfortunately your DME solution didn’t work.

Going to look for ground issues next.

Anyone else had a similar issue that was resolved with new ignition coils? Or a replacement DME relay? I want to try to avoid dart board new part purchases, if possible.

But, open to any/all suggestions.

Thanks
Chris

You could add cleaning the AFM.

2nd !Bert

Thanks Spokes and Bert.

Have you both had similar symptoms that we’re corrected with cleaning the AFM or does it need to be replaced?

I meant to mention that I have replaced the ISV - just to confirm these are 2 different and distinct parts?

Thanks
Chris

The AFM is 30 some years old I would try cleaning it first and a fuel filter if not already replaced ..
thanks Bert

964 stalling and rough idle
 

This may sound crazy but I had the same problem on my '93 C2 and it was caused by an aftermarket carpet that slid forward against the gas pedal. I went down the same road as you described to no avail but, on a whim, I took the carpet out and everything returned to normal. I know this was the cause because it happened a second time.
I'm embarrassed to offer this explanation but, hey, it's easy to give it a try if you have the same situation as me.

Seconding the carpet issue!
 

Went around and around with this one with our 93 RSA and it ended up being a floor mat that pushe on the gas pedal just enough to mess with the microswitch.

Thanks. I just sent the floor mat suggestion off to my local shop, Turn 3, to check.

This one seems to have them stumped. Very stumped.

Chris