'99 Mustang GT high idle problem

[stangman16]

'99 Mustang GT, all stock except for flowmasters

Okay, I did use the search function, and after changing the IAC (which kind of helped the problem, but also made it worse) and now changing the TPS... I am stumped.

with the AC off, when I press on the clutch to idle towards my stop, my car idles at 1800 rpms, and when the car comes to a complete stop it'll idle at about 1500 rpms. With the AC on it'll idle at 1200 rpms.

Anyone have any suggestions on what the problem is? I've tried knocking on the IAC to see if that helps, but it does nothing, and the car still idles high after a new IAC and TPS.

I cannot remember exactly when all this started happening, probably a month ago, and in April I had my car taken in for the intake replacement before my 7 year period was up...

Any help would be great. Thanks!


EDIT: I did visually check for vacuum leaks, and I couldn't find any...

 

[stangman16]

also, when coasting the idle fluctuates from 1200 to 1600 rpms... until I get to about 15 mph then it'll stay at 1800 rpms

 

[RedDaemon]

MAF?

 

[stangman16]

before I go spend more $$$ on a MAF, is there anyway to be sure that is the culprit?

Any way to test it?

 

[RedDaemon]

clean it..see what happens

 

[jstreet0204]

FIRST!!!!
Tap your IAC valve with a wrench. Most likely your problem is that it is sticking. Tapping it will usually knock it loose. If that doesn't work, try taking it off and cleaning it with some carb cleaner. The MAF shouldn't cause a high idle. A dirty MAF will usually cause a rough idle.

 

[stangman16]

well, I decided to take off the IAC restrictor plate that I've had on there for 10K+ miles with no problems, and now it idles just fine. I'm not happy with the slow dropping RPM's, as that's why I bought the restrictor plate, but at least it works fine now. I don't see why out of the blue the restictor plate would cause the engine to idle high and fluctuate the rpm's while coasting.

I guess I will save up for a xcal2 tuner sometime and fix the idle decay correctly.

Thanks for the help. If you have any suggestions as to why the restrictor plate would cause it to act like this, when I had no previous problems during the 10K+ miles I've had it on there, I would still love to know.

 

[SilverBullet00]

Thats what my car is doing now, but I dont have a restrictor plate on mine...

Glad you got it fixed! Maybe one day I will figure out mine!

 

[madmatt]

LOL seems to be a common problem, mine had been doing it for about 2 weeks now. I cleaned it with carb cleaner and it seems to have worked. We'll see...