GM2Ford

So I'm new to the Mustang world. I'm make sure I don't leave anything out. Please read it all! Thank you!

I just bought a 1999 GT 5spd with 154k a week ago. The car runs great! SO here's the issue. About 4 days later, It has a K/N Cold Air Filter on it but it looked a little dirty. So I decided to clean it with the proper K/N Recharger Kit. Along with that I decided to clean the TB a little as well... So over night I let the K/N Filter dry with the new oil on it. After I put it on my brother noticed that I put too much oil on the filter. He said "You, know it's going to suck up and get on the throttle plate now." I said "okay," I took it for a spin everything seemed fine and was running perfect until the next day I started it up to REV the engine.

Here's the problem.

I start up the car and the rpms come down a bit slower than what normally I was used too. So as I rev the engine to about 3000rpms it takes about 4 seconds to get down too 1500rpms and then hangs there for about a second or 2 and then goes to 1100-950rpms. What the hell?

I've been reading forums and everyone says... Clean the IAC with carb cleaner. Check. Clean the TB again. Check. Spray the MAF with MAF cleaner. Check. Look for vacuum leaks... I made sure I took everything off that I did and put it back nice and tight. No leaks. I even sprayed Carb cleaner around the hoses end points to see if it would suck it up or notice a heistate in the engine speed. Nothing. Check.

I made sure I cleaned everything nice! Tightened everything up nice! Someone even said because of the "too much" oil I put on the filter could be getting on the MAF or other parts causing it to read funny. So I took everything off, cleaned it AGAIN! Nothing. I even disconnected the battery for 30mins, depressed the break pedal 4 times and flicked the headlights switch on to drain the left over juice in the car after the disconnection.

I start the car up. Nothing! The rpms still hang there. I even took it for a spin and when I press the clutch to switch gears the rpms hardly move (eventually they drop) inbetween gears.

When I unplugged the IAC after all this the car seems not have the hanging rpms effect when I rev it. But when I plug it up, it hangs and it's driving me crazy. It sounds so weird. The throttle is not sticking or the pedal. I made sure, I also rev'd the car with my hand at the throttle and pushed it back to make sure it was closing and it still was hanging at about 1500rpms and slowly dropping.

Is there anything I can do to fix this? Also, why isn't my car idling back at 800rpms where it was yesterday before I did this? Could this hanging rpm be causing that as well? Again, none of this happened until I decided to clean my TB & my K/N air filter.

cliffyk

Check the throttle stop screw adjustment, all that cleaning might have gotten things so clean that there is too much air bleed at "closed" throttle.

With the IAC unplugged the idle speed should drop noticeably, and perhaps even stall; if the throttle is too far open when closed it would behave as you described. This is a critical setting as the PCM expects a specific airflow through the TB at "closed" throttle. I.e. just enough to keep the engine barely idling so that it can then use the IAC to adjust the idle up or down as needed.

In normal hot engine operation--no added load from the fans, generator, p/s, AC etc.--the IAC is held 35% to 40% open by a variable duty cycle square wave supplied by the PCM.

Here's the PCM supplied signal for my '03 at idle as described: