ECC keeps learning bad idle??

[MalcolmV8]

Hey Guys,

I've been trying to help a buddy of mine get his Mustang running right. It's a 2000 with some basic mods, bbk TB 78mm, CAI, exhaust (catless), bbk long tubes. 3:73 gears too but I doubt that has anything to do with this issue. Stock heads and cam as best we know (he bought the car used).

The issue is if you reset the computer by disconnecting the battery or if you reflash the ECC with his hand held the car runs perfectly. However after a day or two the computer changes its idle strategy and doesn't hardly want to idle the car at all. It keeps stalling. If you blip the throttle real quick and easy it will often rev up and then go so low it'll almost die or will die.
You turn the steering wheel hard while sitting at idle and or turn on a/c and often it will die cause the idle is not strong enough.

He got a custom tune via mail order with specs on his car (against my advice) and had them bump up base idle. It works just fine when first loaded on there but as soon as the ECC learns some parameters the idle goes to crap.

So I opened up his throttle body a tad with the set screw so his car could idle with the IAC unplugged. It's a low idle just to keep the engine alive. You plug the IAC in and the idle goes to normal speed. However after a few days of driving the ECC has learnt that crappy idle again. It bogs down real bad all the time again. It mostly doesn't die now since I have the TB slightly open but it still does the same bog.

He's replaced the O2 sensors twice now. Replaced the IAC and a few other basics. Any ideas on what I need to be looking for? Car has no codes yet somehow over a few days will learn a horrible idle.

[cgrey8]

If it's a mail order tune, it probably has all the "codes" disabled or the limits extended out so far that you couldn't make it trip a CEL if you wanted it to. That's often what people trying to pass emissions want. But it does make diagnosing a PITA.

Without datalogging or a Wideband to know if it is bogging/hunting due to rich or lean, I couldn't say. But ultimately it doesn't sound like a mechanical problem. It sounds like a TUNE problem particularly if it will run right when the EEC is cleared, but then learns the bad behavior.

[MalcolmV8]

I could be wrong but I'm thinking he didn't get codes on the stock tune either. I'll have to go back and validate with him. I agree it sounds like a tune but the stock tune was doing the exact same thing. Car runs great when ECC reset, just after a while it learns this horrible idle.

Unfortunately he has no wideband or data logging of sorts.

[Soul]

What about the tps?