HasABetterSN

Hey guys - so the past couple months I've been having some problems with my 2002 Mustang GT idling. (I have done a number of searches on here, and tried a couple things I found, with no improvement).

So this all started with it sounding like a French horn while idling - indicative of a failing IAC. So I replaced the IAC with one I bought at O'Reilly's auto parts. After replacing the old faulty one, and clearing my KAM, my car would idle around 1k - not good, but no more French horn under my hood. I went back to O'Reilly's and exchanged it for a new IAC, thinking that the new one may have been a little faulty itself. The second new IAC, however, still idled at 1k - so in an attempt to put a bandaid on the situation (so I could get to work) I put a copper pipe cap in the vacuum line leading to the IAC to restrict the air flow, so the idle would be at the right spot. Note - with the pipe cap, I cant use the A/C or defroster, as the idle would dip to sub 500 because the IAC would not compensate for it. Next, I replaced the TPS and cleaned the MAF in hopes that it would idle correctly - but no improvement was seen with these. I also checked the vacuum lines, and as far as I can tell they're fine.

Now it runs fine with the copper pipe cap bandaid - but I'd still prefer to fix it completely before summer, so I can use the AC. Do you guys have any idea what the problem may be at this point? I would rather avoid taking it to a mechanic, since I have no other way to get to work. Sorry about this being a little wordy, I just wanted to provide all the info I could (my mods are in my sig as well).

Thanks in advance!

The02GT

Sounds like a vac leak somewhere

petrock

So let me get this straight, you capped the vacuum line that controls the IAC and the car idles normal. Correct? Then you have a vacuum leak somewhere between the throttle body & cylinders. Otherwise the car would stall. Its probably the throttle plate not fully closing or an upper/lower intake manifold leak. Good luck...

HasABetterSN

I didnt quite cap it - I just restricted the air flow a bit (its what people do for the hanging RPM mod as well - I drilled a hole in the copper pipe cap). Thanks for the suggestions guys, I'll have to take it in somewhere and have them test for any vacuum leaks then.