Idle

[buffluv]

I am having an idle problem, on cold starts it will rev up and down between 500 and 1500 rpm. After it is warm there are no problems, it will drive fine, idle fine and start and idle fine. I replaced the vacuum lines and the idle control valve and still no difference. Could the vacuum lines hooked up improperly cause this problem? How does the car see engine temp and adjust for fast idle?

[mikepellegrini]

The idle hunts up and down?

My guess would be a vacuum leak where a metal tube fits on to a rubber or silicone hose. As the car warms up, the metal expands and the leak closes?

I believe the Idle Control valve adjusts the idle. I s'pose it's possible you got a bad one - that does happen. I'm not sure what kind of behavior they exhibit when they fail.

I would think if you'd hooked the hoses up wrong, it probably wouldn't run (or at least would run badly).

Here's a link to a vacuum hose diagram, if you haven't seen it already. Porsche 951 (944 turbo) reference list

I've got somewhat the same problem on my 951 - for the first five minutes when it's cold, it idles about 2K. It started this maybe a week after I re-did all the vacuum hoses under the manifold.

It runs great otherwise, so I haven't done anything about it yet.

[buffluv]

Yes its a hunting idle, and really it doesnt take the car to get warm to stop, it does it like the first minute. The old idle control unit did the same thing thats why I replaced it. I was thinking a temp sensor was faulty and not showing the computer it is cold. During this hunting idle if the gas is pressed it revs right up, maybe im expecting this old lady to act like a new car.