When I start the 944, it idles at about 950 RPM where it should. As the car warms up, the idle will raise and settle at about 1200 RPM when it's warmed up.

Does anyone have any ideas why?

FYI:
The speed and reference sensors are new.

 

Mine does exactly the same thing. The only idea I've had is that once the oxygen sensor comes to full temp, it stops using the pre-loaded data and actually uses the O2 sensor's input for fuel mixture reading.

My car can feel really violent at the lower RPM too before it warms up. Yours see this? The steering wheel and most of the dash actually vibrates enough to be visible. Once warm, the car idles around 1100RPM though and the vibration isn't apparent. Only at ~900 is it.

 

Mine actually runs really smooth, it's just idling faster than usual. I'm starting to wonder if the AFM needs replaced.

By violent, do you mean it feels like it's stuttering or hesitating? That's caused by the speed/reference sensors (or was on mine).

 

Violent shaking. The idle is constant and very settled at ~850-900RPM. The steering wheel is shaking though, as is the dash. If I touch the gas even slightly and revv the engine up to 1000+, the car gets really quiet and fine. But below 1000rpm, the front end seems to shake pretty nuts. There's no other shaking at any rpm, which leads me to believe that it's not a balance belt issue (timing or condition), but rather just a resonance vibration I'm feeling through the steering shaft. What might cause this?

 

I have the exact same problem and it is driving me up the wall!!!!
The throttle is also extremely sensitive when I am at idle, like it is impossible for me to rev the engine up another 100 rpm's its 300 up from idle, idle, or regular driving speeds

 

That sounds like it might be a throttle positioning switch sticking.

 

Maybe I'll replace the TPS.

For now I'm also trying to save for a truck and I'm going to have my friend's neighbor respray the hood back to the hatch (all the horizontal panels) where the clearcoat is screwed up... he quoted me $200 + materials and does nice work. With all that I'm not replacing anything expensive at least till I get the truck for a DD, so I'll see how it all works out...

 

I need to do my hood as well. The clear coat is peeling by the square inch. I also need the front valence done, as well as the front fenders so i'm looking at a huge bill.

As for the idling, the TPS is really easy job. Taking the throttle off takes longer than inspecting and cleaning (and testing) the switch. We did it in about 10 minutes...fixed it from "switch reading closed all the time" to "functioning properly". The contacts were bent, and when the throttle was closed (idle), it was reading closed. But when open, it was hanging on the contact for closed far too long.

 

would that be a problem that happens all of a sudden? like one morning you start your car and it does that?

 

This sounds like the Idle Stabilizer Valve is dirty and sticking. My 83 did this at start up. Does the car stay at 1200 rpm indefinitely, or just when you start warming it up?

Try removing the ISV and cleaning it out with WD-40. It's a bit@# to get to under the intake manifold, but it can be done without removing it.

 

When I start the car and it is cold, it will idle right around 900-950.
As the car warms up the idle slowly seems to raise, once it reaches operating temperature it will idle at between 1050-1150 and stay there indefinitely. If i turn the a/c on after the car reaches operating temp. it will drop to a very rough 750-800 and as the pump cycles on and off the idle raises and lowers.

Does this sound like a TPS problem or a ISV problem?

Terribly sorry RMills944 for the hyjack

 

^^ No, you described what mine is doing perfectly (other than the A/C part... haven't turned that on in years)!

 

I removed the j-boot today and sprayed a ton of carb cleaner down the ISV line and let it sit for about ten minutes. After I drained the remaining fluid out of the line, I put everything back together and started the car. Sadly I think my ISV is dead... or I just didnt do a thorough enough job cleaning it. Tomorrow I hope to physically take the valve off and play with the idle. And then just to be on the safe side I will also check the compression on each cylinder.
Also MRills944 currently I dont have a working fan switch so I use the a/c to turn on the auxiliary cooling fan. But I will keep everyone informed.
What should the compression specs be?

 

Look up on clark's garage how to bypass the ISV electronically - it is really easy to do. This should shed some light on the situation- of course, how warm the car is when you bypass the ISV will determine what position the ISV stays bypassed in. But if the idle stops moving all over the place when you bypass the ISV...you probably have your culprit. I'm seriously considering installing an ISV bypass switch and routing it to the dash. Using the low-speed air screw on the throttle body, once the car is up to temp, you can get a nice smooth idle without that "dip" at idle return once the ISV is turned off.

 

My advice would be to replace the ISV and TPS, and set your idle via the factory manual (disconnect the 02 sensor and bypass the ICV) and if you can get to a 3 or 5 gas tester set your CO it really makes a HUGE difference if you do this. Had a guy at work do this recently to his 951 and he gained about a 100 miles to a tank of gas and his idle is ROCK solid from cold to warm.

Mark