I ahve been battling this for months. The engine is smooth at 1300 RPM. but driving in the city is a pain.
I have set the TPS. played with the idle speed screw, BAC, and idle air control. If I'm able to get the idle around 800 or 900 RPM, it will be a little rough. but if I let it sit and cool a bit, the next time i start it the idle with either be back at 1200 or so, or the idle will bounce, or both.
I am frustrated. the more I try and fail the more frustrated i get.

FYI I have removed the hard vac lines under the UIM and everything associated with it. But I have had this problem before I did that. I was hoping that removing it would help fix this. EGR is also gone. the thermowax on the throttle body is still there but has no vac lines.

The car won't pass emissions with such a fast idle, and I need to get my tags.

I'm beginning to think an engine fire would alleviate my problems.

 

I presume you mean coolant line. There's your problem. You can either rotate up the thing that touches the thermowax and zip tie it in place, you can remove the fast idle cam altogether, or you can reinstall the coolant hose so the idle will come down.

 

It's freak'in stupid. I never get the same results twice.
I took off the throttle body and thoroughly cleaned it. I removed the fast idle cam and adjusted the screw on the back side of the TB linkage. Reinstalled and it still was idling at 1400. played with the idle air screw and BAC to get it back down to about 900. running rough as hell and fluctuating about 150 RPM. at part throttle it still surges. at this point I realized that i forgot to turn on my e-fan. so I turned that on and let it cool a few degrees. when i started it again (about 5 minutes later) the idle was super low and surging. I played with the screws again to smooth it out and it's fast, but still does the part throttle surging. I have video. The second vid is hard to hear with all the fan noise. butI am holding the throttle open slightly and holding it for a few seconds. then i moved it ever so slightly open and hold it there for a few seconds. I move it open about four times. if it's not fully closed or about half open, it surges.

 

now that it is completely cold. with all of the adjustments I have done it won't idle. I have to hold the accelerator to keep it running. I didn't bother getting it completely warm. I just wanted to make sure it was more screwed up than it was yesterday.

 

no one has anything to add or suggest? I really don't want to replace every part of the fuel system. but that is the only thing I can think of.

 

it sounds like you just don't fully understand how the idle control system works. with the fast idle cam removed, it's not going to idle well when cold unless you raise your base idle pretty high. the fast idle cam opens the throttle plates when the engine is cold, and then rotates them back to their normal position, resting against the stop screw.

When warm, you set the basic throttle opening angle with the stop screw (I don't know where it is on the n/a TB, my n/a never had many idle problems). then you make fine adjustments by turning the screw on top of the manifold (n/a) or on the BAC (turbo). You have to have the initial set coupler jumpered though when you make idle adjustments, or the ECU will try to fight your adjustments with the BAC. You also need to have your TPS and your timing set properly (along with no vacuum leaks etc). The variable resistor is also there for s4's to set the mixture, and that also affects the idle speed some. Have you tried to follow the factory idle set procedure in the FSM?

 

ok, I understand most of that. i have read the FSM. I have owned one or more FCs for over 12 years and never had this bad of an idle problem.
I removed all of the vac lines I could to eliminate as many possible leaks. I replaced all remaining vac lines with new. But before I did this i sprayed the thing everywhere with ether first, then carb cleaner. I never found a vac leak.

I went and pulled three throttle bodies and two UIMs from storage last night. I'm going to test sensors and find good ones to install. I suspect that the TPS is slightly out of whack, but I'm going to replace the others too just to be safe.

 

Ok, so I replaced the TPS, the air intake temp sensor, and I put silicone on the plastic TB spacer.
Got it running finally. when I first put it all back together and fired it up, it was still acting like it had a vac leak. it did. I had knocked off the hose to the cruise control. fixed that and set the idle speed. It's not as rock solid as it should be. it fluctuates about 50 RPM. but I am much happier. I may have to re-install the cold idle cam. it's about to get much colder here so i will just wait and see. right now it's not too bad, but i think I'm probably going to.