Idle problems.

[TheRoadVirus]

I'm trying to figure out what's causing my truck to idle all over the place. I've replaced the tps after checking it (out of range), and throttle response improved.. which was nice. I've also replaced the IAC because it was said to be the cause of my fluctuating/rising idle, after taking it apart and finding it all messed up I replaced it. Thing is, it didn't fix it!

I didn't bother returning it and I assumed it must be something else as well - never ends. Plus my trucks in the garage for the winter so this isn't a pressing issue, but I would like to get it fixed. But now that it's in the garage there's a noise from the throttle area that I didn't hear when it was outside. I'm sure it helps that the intake system is off right now as well. But this whooshing sort of noise only happens right before the idle rises and disappears when it returns to normal rpm. I'm assuming this would be my IAC opening and closing.

So what exactly tells the IAC to open and close? My o2 broke and I haven't been able to get it out with any persuasion so I'm just planning on replacing it with the new set of headers I'm getting (mine are toasted) could this be my problem?

I'm almost done.. one last thing.. it doesn't ALWAYS do this.. it seems to be fine sometimes and then goes crazy other times.

Hopefully I diagnosed it well enough. Thanks in advance guys.

 

[F150]

Did you try this?
http://www.muscularmustangs.com/idlereset.php

 

[bowtiehatr]

have you checked for vacuum leaks? the upper to lower intake gasket is bad about sucking in and can cause what you are describing.

 

[TheRoadVirus]

And that would cause the IAC to open and close? I guess it would be adjusting trying to maintain a certain idle or what?

Also; F150 I've heard about that before but I wouldn't think that it would cause my idle to be hunting all over at times. If my idle was high or low then I could see doing that, but my truck idles perfectly at times and goes crazy fluctuating sometimes as well.

 

[blacksnapon]

Fuel injected vehicles use vacuum management to adjust the idle. When there is a vacuum leak, the engine has double the problems to stabilize the idle speed.