Would 02 sensors cause erratic idle at first then smooth out? When cold, my truck idles like dog ****, then smoothes out within a minute. I'm not getting a 02 code so i don't know for sure. Thanks for any help -Mike-

 

If it helps any, i recorded a sound clip of my truck at cold idle. Sorry for the wind in the background, i hope you get the idea anyway -Mike-

http://www.generationblueoval.com/ga...lbum=18&pos=54

 

Its your IAC valve, mine did the same exact thing....Does it hum to when its warmed up?....Mine fires up rough like yours when its cold, idels at 500rpm's then snaps out of it.

The same exact thing happened to me and it was my IAC valve, it cost me $74.99 at Autozone here in NH

 

well i have no CE light so if it's a sensor, hard telling. I recently had it scanned at AZ and no codes. About 2 months ago, when i replaced my TPS, i cleaned out the IAC. Wasn't gummed up too bad with oil and junk but enough for it deserve some attention. I cleaned it out with carb cleaner. It didn't help the rough idle any though. That doesn't mean my IAC is still bad though. Guess it's one of those guess n check situations -Mike-

 

Trust me its the IAC, i couldnt bring myself to belive it either but thats what it is...If it starts up and idels rough, and hums, thats what it is.....put a new one on and itll cure all your issues. Cleaning it is temporary. It lasts a couple days, even hours.

 

Yea I'm pretty much convinced that's what it is. I just had a good buddy of mine verify that and let him hear the recording. Next paycheck i'll get one from the Ford dealer and hopings that's it.

Now that I think about it, that's really the only the other thing that controls the engine speed w/o the throttle. Thanks man! -Mike-

 

I suspect my rough idle is because of an exhaust leak at the header flange (haven't had a chance to put the truck on the lift to see if its damaged of if the bolts are just loose.) I suspect the leak before the O2 sensor is causing it to read a lean condition, so the computer is richening the AFR, choking the motor at idle, and probably causing my recent drop in MPG.

Before you ask, I know I have a leak because I tried running some top engine cleaner through it as a cheap pot-shot at the rough idle, and a fair amount of smoke came out of the collector/flange instead of the exhaust.