mustang_montana

who is that to? im the one that said it was NOT the iac. it is definetly o2 sensor related, which is what i said in every post i made. sometimes its like people dont even read the replies, case is closed its the before cat o2 sensors.

deathblooms

thanks for all the input guys! im going to have both the IAC and the Cats checked out. Im also leaning toward the IAC after doing alittle research on them, and reading the problems a car will have when it goes bad, and so far my problems match up with the IAC perfectly., heres a small list of problems when it goes bad:

The Idle air control (a.k.a. IAC) bypass valve is an electric motor attached to the intake plenum that routes air back to the intake tube when you let off the throttle (when throttlebody closes).

Symptoms:
- car shuts off while driving, especially after pushing in clutch, letting off gas. (happens to me only im an auto, fun to take of at 2500 rpms trying to keep the car running)
- on cold starts, it won't idle unless you keep your foot on the gas. (happened at auto zone and every other cold start ive had)
- infrequently does this at first, and progressively gets worse. (When i first noticed this was last summer, the car would start really weak, and now its got to the point were you cant keep it running without keeping your foot on the gas.)

mustang_montana

you said it was surging while driving though, thats not the iac. so replace it if you want but im sticking with my first answer. check into the o2 sensors because those are what got moved around during your header instal, the iac wasnt touched. go ahead and throw 60$ at a new iac though, cant hurt. but seriously check your o2 sensors, the front 2. you might need to get 2 new ones, like bosch widebands. are they the stock o2s?

deathblooms

i know we used two of the stock 02's, i dont remember if there the fronts or the rears, i couldnt hurt to replace all the 02's with some widebands, and replace the IAC, this way i get the best of both worlds

Biltsy

IAC has nothing to do with your problem. IAC only contributes to supporting airflow to the upper when at idle. Unplug it, and rev up the engine, you'll see the rev's droprapidly, nearly to a stall. Your O2 sensors are reading new. I agree, take off and cleaning the IAC and MAF are good ideas, can't hurt. The problem is, the 02 sensors will advance / retart timing for emissions. Since you've replaced your headers, the computer needs to re-learn. Do youself a favour, and have the PCU re-flashed. Your dealer can do it in about 3 minutes. You'll also be able to take advantage of any new codes or upgrades Fords' have installed since your car's birthday.