Idle Issue

I have a 01 GT with a 70mm TB and Accufab plenum. The thing has worked fine for 2 years. The other day I was cleaning out the throttle body with TB spray and when I reassembled it it began to idle very high. When the car is warm on stock tune, car idles around 1000 and on my SCT 93+ tune it idles at about 1500. I cleaned and then replaced the IAC solenoid and the problem persists. I fidgeted with the set screw but it had no effect. I didn't adjust the TPS ever... what could be causing this problem?

After you clean the TB you should reset the PCM to allow the car to relearn the fuel trims.

I did, I flashed the computer

sounds like a vacumn leak, check the pvc hose, plenum, and IAC hose and
make sure they are in the right place and tight

and did you try disconnecting the battery, wait about 15 minutes, then starting?

Quick PCM idle re-learn procedure.

There is a procedure to speed up the re-learning process. Start and idle for 1 full minute with the AC off. Next turn on the AC and let idle for 1 full minute.

The PCM re-leaning is done to account for differences in motor wear, temperature, gas, and such.

I had a 96 that you could not get out of the driveway after the battery was removed until the quick learn procedure was done. Then it was fine.

As a double check, monitor the IAC % and verify that it changes when the AC is turned on/off. Also, it should be around 50%. If way low, may be vac leak.

Also, if you adjusted the stop on the TB, suggest that you put it back. The TB needs to allow only a very small amount (almost none) of air to pass. The bulk has to come from the IAC.

As a basic IAC function check, disconnect the electrical connector to the IAC. If dies right away, it is basically working. If it continues to run, the IAC is not adjusting, or there is a vacuum leak, or the TB butterfly valve is not closing enough.

That I did not try... is that different from flashing?

All vaccum hoses are tight, I adjusted the set screw 1.5 turns past contact with the arm, and i will leave the battery unplugged for 30 mins. Hope that does it

In many modern engines, the throttle plate is designed to be a nearly air-tight fit when closed and all idle control is performed by bypassing the throttle plate with an idle air control (IAC) valve controlled by a solenoid. The sealing of the throttle plate is very often done with a silicone elastomer applied to the inner bore of the throttle body; when the plate closes, it closes against this thin elastomer forming a good seal. For the OE part, Ford's service manual recommends against cleaning the bore:

"CAUTION: The throttle body bore and plate area have a special coating and cannot be cleaned." - 2002 Mustang workshop manual, p. 303-04B-5

I suspect the Accufab part will have a similar coating on it for the same reason. When you go in there with a high-pressure solvent and/or a bristle brush, you likely remove some or all of the seal which allows uncommanded air past the throttle plate, increasing the idle speed.

The PCM may or may not be able to compensate for or "learn" this additional air. If it doesn't you might have to try putting a seal back in by roughing up the surface of the TB bore where the TP closes with some 180-grit sandpaper, degreasing it thoroughly and then smearing in a very, very thin coat of O2-sensor friendly RTV. Let it cure fully before allowing the throttle to close.

It could be your tps.

Problem started when you decided to clean something that really doesn't need cleaning. And as Trinity points out, you've likely ruined the coating on the butterfly...Accufab DOES have the same type of coating like the OEM throttle body that SHOULD NOT be cleaned with any type of solvent.
I'd go through the motions of trying to get a proper 'reset' before attempting any other methods to resolve this issue. Seems to me that adding RTV, albeit a "very, very thin" coating, still could cause havoc if it decides to let go and head into the combustion chamber...probably would burn right off, but...never know...!

Put your stock TB back on and see what happens, if you still have it.

It's still idling high at about 1000-900 RPMS. The TB spray states that it is safe for throttle bodies... so now what? Do I need a new throttle body?

I've cleaned plenty of throttle bodies before and this has never happened?

It's your TPS. Do you have hard starts? Idle surge? stange power dips while driving?

Car drives fine, no surges. I put the stock TB back on and the car idles normally at about 650-700 RPMs now. I sent the Accufab TB back to them for a rebuild ($75) and hopefully that fixes the problem. If I get it back and it's still idling high, I'll adjust the TPS next I guess. Remember, this only happened after I cleaned the TB...