[wyldstallyns]

Hi you guys, New to the forum

Anyways on to the question. 2003 Mustang GT.
Why is it when my ac is on, the car idles absolutely perfect. but if i turnd the ac off, my cars spits and sputters.
The car is perfectly fine, all tuned up. the only thing out of date is the front 02's. but if they were bad, why would it idle so perfect with the ac on?

Dumb question? GET OVER IT its the internet haha

[realrider88]

change the belt and o2s

[JerseyTrueBlue]

Screw the O2's, your problem sounds like a dirty IAC (idle air control) valve. You could try cleaning it with something like MAF cleaner and see if this fixes the problem. If not you might have to replace it like I did. My car died when I turned the A/C on instead of off, but the IAC is a common occurance on these cars.

[neverfastenough1]

Don't turn the a/c off, problem solved! I am good, huh. You idle picks up every time your compressor kicks in, at least thats how it works on a stick because the idle is lower than an automatic. An automatic is idled a little higher to keep it running smooth when in gear and the brake applied. Again, at least thats how it works on foxbodies. Thats why its not recommended to use a computer from a stick in an auto (foxbody). I would try the iac cleansing and while you are at it, wouldn't hurt to clean the maf and change the air filter if its old.

[wyldstallyns]

leave the ac on huh? you see that becomes a problem during winter.
like i said, the car is tip top, i keep my throttle plate, plenum, and idle control motor clean, i check it every 10xxx
maybe ill replace the iac though. its just weird, my car has never idled well. i could understand a little rough, but mine just gets plain nasty sometimes