Idle Problem

[944Repp]

I have a 1984 Porsche 944 that has idle problems.
It starts up fine, but after about a minute it begins to idle up and down from about 800-1200 rpm. It drives fine, no other apparent problems. Until you pull up to a stop sign.

The car has 85,000 miles, no apparent vacuum leaks. The large intake elbow hose has been replaced recently. All hoses seem to be tight, etc...Prior to last week, it drove fine.

[Stoutpants]

I've had the same problem with mine when it's really cold (25f or less) Once the engine has a chance to properly warm up then it idles just fine. I'm not sure what to do about it though.

[BrianT]

I am having the same problem with mine. It will start fine, run fine, I am right now in the process of cleaning the grounds on the engine, I did find them to be very croded. I will see if that helps. I saw the problem the other day and adjusted the idle down a little and it looked like it solved the problem, but it came back. If the ground thing does not work I have a O2 sensor to replace the old one. May be that will fix it.

[Razorback1980]

Check the throttle position switch to make sure it's working and adjusted correctly. Check out clarks-garage.com for a complete description on how to do this. The auxiliary air valve is another possiblity. Wait for the car to start this and then clamp the hose. If it runs differently then that might be the problem. The other thing I can think of that might cause this is the DME temperature sensor located on the block.

944 repp...welcome to the forum and check out these links for information about your car.

clarks garage as already mentioned
http://www.connactivity.com/~kgross/FAQ/944faq05.html

[Razorback1980]

Stoutpants, yours is probably the DME temperature sensor. It's located on the engine (front left just under the cylinder head IIRC) ...let me know if you need help finding it.

[BrianT]

Tom, I will try the aux air valve It does not do this all the time so I will have to catch it when it happens. I have replaced the throttle possion switch and adjusted it using Clarks Garage specs. It is working, I can hear it click and also checked it with a ohm meter. I replaced all the vacuum hoses and maybe when I was in their I may have damaged it somehow.
Thanks for the info.

[Stoutpants]

Thanks for the advice razorback. I'll probably try to tackle this early next week (when we're supposed to get above 40) and I'll probably need all the help I can get.

I'm guessing I would need to replace sensor. Or is there something else I would need to do to the sensor?

[Lawrence Coppari]

I had an idle problem once - a lot of stumbling until the engine ran for 15-20 seconds or so. In my case it was the idle stabilizer valve. Attached is a picture of it. Try pinching the hose like previous poster suggested. Valve is a little pricey.

[Rick V]

I finally tracked down my high idke problem...................When I assembled the engine I advanced the cams (shift the powerband). The DME can't figure it out..........................................high idle.

[thekidd]

Mine was idleing like that too, idle at 850 poped to about 17, 18 grand then to 850, then to 16, 17 grand right away. never found the problem though. RIP my 855 944. hopefully will resurec

[SoCal Driver]

The idle hit 18 grand? Amazing! Perhaps your decimal is off a place or two.

First thing one needs to look at is the year and model of the Original Posters car; 84 N/A. Single cam, basic heated idle valve.

First thing I would do is remove and clean the throttle switch, reinstall and adjust it. The throttle butterfly valve mechanical stop should not be adjusted to set the idle. The air bleed by needle valve (large screw) is the idle speed adjustment. This over size screw has an o-ring that should be checked and replace as needed.

If this does not stop the idle hunting then start looking for a vacuum leak. Could be something simple like the J-boot or something obscure such as the brake booster diaphragm.

[thekidd]

ok, maybee not 18, but it went way up there to at least 16 every time when i started her in cold weather, the only wether i had her for. Then after about 10 miuets or so it would stop, then id go riding