944 starts then dies if I take my foot off the gas

[9fourteen]

I was getting ready to do some brake work on my 944 this morning and when I started it up, it started right up but when i took my foot off the gas it died. I can keep it running and seems to run fine just as long as i don't release the gas. It will not idle. It ran fine last week when I had it out. I have not done any troubleshooting yet. I am guessing DME or ignition switch based upon what I have read so far. Anything else I should check?

I have a spare DME relay so i will probably start with that.

[944 Ecology]

Look for a vacuum leak.

[9fourteen]

not sure what the problem was but it seems to be running fine now. I replaced the DME relay but it didn't fix the problem. Checked the cold resistance on the DME temp sensor and everything tested out ok within the expected range. I was checking for vacuum leaks. I rigged the throttle to stay open a bit so the car would keep running after I started it so I could listen for leaks. Not sure if that is the best way to find vacuum leaks but it made logical sense. Anyways, after a while of revving it up it would idle and not stall but run really rough. I was thinking maybe the DME temp sensor could still be messed up so the second test on it was to do it with the engine hot. So I was revving it up hard trying to warm it up. I hit about 6000 RPMs and it made like a popping sound like something broke free and then it ran fine from that point forward. Not sure where the sound came from. Sounded like the exhaust but that could have just been it finally running right and the tone changing. I am leaning towards maybe something in the fuel line and that was restricting fuel flow and by opening it up a bit pushed whatever it was through. Don't know. Hopefully it won't return whatever it was.

[gtroth]

I'd make sure your TPS is operating as it should (DME may not be getting the message that it's time to idle...).

Where did your idle speed end up with your rigged throttle (what does it take to prevent stalling?)?

[9fourteen]

Originally Posted by gtroth

I'd make sure your TPS is operating as it should (DME may not be getting the message that it's time to idle...).

Where did your idle speed end up with your rigged throttle (what does it take to prevent stalling?)?

Like I said it is all running normal right now without the throttle being rigged. When I had it rigged I just propped the throttle open slightly by unseating the throttle cable so there was a little tension on it. As soon as I got around to the engine compartment I reseated the cable and then operated the throttle manually by hand. I did not leave it rigged up for more than a few seconds. It was just temporary for me to get the car started and around to the engine. Once it warmed up it was running without it being rigged up. I don't recall the RPMs when it was idling rough but I think they were low. Once I "blew it out" it was running smoothly at about 900 RPMs at idle.

[Jfrahm]

Wouldn't the idle air controller be worth a look?

[JxJ]

I had the same problem on my 1990 944S2. The most common problems are:
Vacuum Leaks
Idle Control Valve (ICV)
Throttle Position Sensor (TPS)

In my case it was an intermittent TPS. On most of the non turbo models it seems there is a switch that closes when the throttle is closed to idle. If this switch is not making contact it will not put the idle mix and ICV into the right mode and the car will idle erratically and/or die. Mine would only do this when hot, worked perfect when cold out. You may have a temp related TPS intermittent problem too. May work fine hot or cold but not vice versa.

You can check the TPS with a simple ohm meter in just a few minutes. I think the procedure is a Clark's Garage. Basically it has two modes and idle switch close and a near full throttle at less than 10 ohms across separate pins IIRC. You may have to check it cold and then again when the engine compartment is hot to see if it is showing different depending on heat.

One other item to consider but not usually linked directly to idle problems is the O2 sensor. Bosch and Porsche place the lifespan of the O2 sensor at 70K miles. If you have more than that on it it may not be working correctly, again can trouble shoot it with a meter.

[gtroth]

Originally Posted by 9fourteen

Like I said it is all running normal right now without the throttle being rigged. When I had it rigged I just propped the throttle open slightly by unseating the throttle cable so there was a little tension on it. As soon as I got around to the engine compartment I reseated the cable and then operated the throttle manually by hand. I did not leave it rigged up for more than a few seconds. It was just temporary for me to get the car started and around to the engine. Once it warmed up it was running without it being rigged up. I don't recall the RPMs when it was idling rough but I think they were low. Once I "blew it out" it was running smoothly at about 900 RPMs at idle.

Got it. You might have been better off with the problem still presenting itself since who knows where you'll be next time, heh? But at least you have a procedure in that case.

I have another thought on this- the TPS has two switches in it. Idle and WOT (wide open throttle). Maybe while you where reving it you engaged WOT and that got the idle switch to work again. I didn't think that the switches interacted in any way, but maybe. Anyone know?

The popping into good behavior sure has me intrigued...

[Slam]

If your 'pop' had a slightly metallic 'click' to it, then your barn door in the AFM was stuck open and the sound you heard was it releasing. If this was indeed the case it explains everything you describe. Mine did this. Aggravating issue, and I found it almost by accident. I was walking around the front of the car after a run and heard the barn door pop shut.

[9fourteen]

Just an update. I haven't had a problem with the car since. I did a DE this past weekend and the car ran great all weekend. I'm guessing that something was stuck or obstructing and it corrected itself. Hopefully that was all it was and it won't reoccur.