Idle surge '99 GT

[99GT-owner]

U7146
9 r05
Ford Mustang Gt, 1999

After installing the 93 Octane Performance Tune, my car's idle hangs. When I shift, it surges. When I coast to a stop, it hangs and slowly comes down. At start up, the car idles at ~2000 a bit, then slowly returns down to normal idle. The idle in the tune is set somewhere around ~700. Any ideas?

Thanks

[mikel]

Got a CAI on the car?
Does it have a bend in front of the MAF?

Any other mods...?

[99GT-owner]

The car has a K&N. Stock intake pipe. Filter sits right on the K&N. Problem was fine until the new tune was installed.

Off-road H, Flowmaster 40's, short throw, 3.73's, Diablo 93 octane tune.

I am assuming that the Predator is allowing the IAC to stay open longer. If I reset my idle by setting the idle by screw with the IAC unpluged, then plugging it in, will that mess with any of the predator's settings?

[mikel]

Nope, that won't make any changes to the tune.

[99GT-owner]

Good, that is probably what I will do. The guy who had the car before me messed with the idle screw. I had finally got it set exactly where I want it, plugged the IAC back in and reset my idle. The idle was perfect! Now that I installed the tune, its off again. I will try to reset that. If I reset my battery with the tune already installed, will the tune be affected or will everything be ok?

[FordsRuleTheEarth]

That idle screw that your talking about is to set the closed position of the butterfly valve, not idle rpm, thats done with your tuner. Set the "idle screw" so that the buttery fly just touches the throttle body, but not enough to stick. then give your computer time to get the idle right by what you set. If the idle doesn't do what you want, then your IAC (Idle Air Control) valve is bad.

[99GT-owner]

I know. The way I have heard to do it is to unplug the IAC, screw in the "screw" until the car is barely running. Plug in the IAC and reset the computer (take neg. off battery). Let idle for 2 min and drive normal for 15 min. That will reset it to what it should be. I did all of that and it was absolutely perfect! Then, when I installed the tuner, everything is off. I was just wondering if I can do the same process with the tuner installed?

[BlackFalcoN]

I had that problem w/ my 99 ,, I replaced the IAC motor and traced out a peice of tin and the port that goes to the upper intake I drilled a 1/4 inch hole, installed it between 2 IAC mount gasketz and the idle dropped right down 700 rpm quick

[99GT-owner]

For what I have heard, they are notorious for having Idle problems. I just want to make sure that unplugging the battery does not reset my tune... You have to unplug the battery when you mess with idle stuff so that the computer can re-learn it. Is their a function on the predator that allows you to clear the active memory? (the memory that holds all the idle and learned info)

[FordsRuleTheEarth]

You don't need to unplug the battery and no you won't lose your tune. To reset computer go in the diag. menu and reset the engine codes. It does the same thing as unplugging battery, but with out losing radio and other settings. As for setting the "Idle screw. Do it like I said earlier. Set the screw so the butterfly just touches the throttle body. Any more or less will move the throttle position sensor to far and your computer might think it's at part throttle. If it doesn't idle right your IAC is stuck and you need a new one. You may also have a bad TPS (Throttle position sensor). If so measure volts on TPS. Should be 5v at WOT and hardly anything at idle. I wouldn't modify the IAC circuit both air or wires. If the IAC is working properly no matter what your mods. It should idle within 100-150 rpm or so of what you set.

[99GT-owner]

The Idle Air and TPS are both working fine. I just need to dial in my TB set screw.

In the clear engine codes section on the programmer, their is another option under reset codes, what does that do? (9r50)

[FordsRuleTheEarth]

That resets all engine codes and learning tables. The TB screw is the screw that stops the buttery fly. It should be set to just hold the butterfly at full closed position, because of the return spring if it is set so the screw doesn't touch then the throttle will be sticky. At no time should you see any light through butterfly at all at closed throttle, Should be fully seated against throttle body. The IAC should do all the work for idle. If you need to turn the "TB" screw to raise the idle, now the buttery fly is open and your computer thinks your at part throttle, or the computer is seeing closed throttle and way to much air than there should be at idle. In any case if you need the TB screw set so the butter fly is open then your IAC is sticky. When you set the TB screw properly (Without the engine running) and your idle still comes down slowly, the only thing causing is should be a sticky IAC. Iv'e put 3 IAC's on my 97 Ranger 4.0 because of the same issue. Every time, it fixed the problem until enough carbon stuck my IAC again. Never needed on on my 04 stang yet.

[string]

Just do a google search for IAC restrictor. all it does is restrict the flow to the iac and presto!!!! hanging idle gone!!!!!!
I bought one on ebay for $6.00
works like a charm!!!