on the way in to work today i noticed my idle was seriously messed up, sometimes it would idle at 750 (like is usually does) but it would sometimes idle as high as 1300. the wierd part was, a lot of times it would idle up to 1250, then drop to 1000, climb back up to 1250, drop to 1000 and so on. i've tried restarting the car, but that only fixes it for a couple minutes. an idea? bad o2 sensor? bad computer? i'm a work know, and would like to find out something before i have to drive her home.

 

99%: it's a vacuum leak. Did you change to silicon lines or anything like that? Did you put in a bored throttle body? Any mods at all to the intake? If not, there's some ways to find the leak, like using some type of smoke you blow around your intake plenum area to see if it gets sucked in anywhere.

1%: one of the controllers that effect idle air is not working, not plugged in, whatever. Idle Air Control Valve, Fast Idle Valve, TPS is not reading 0 throttle properly.

 

yeah try vaccum like he said. Other then that I turn my idle up to 2grand on race day, eats gas like no tomorrow but it's fun to drive it like that.

 

no mods. my ride is bone stock, and i haven't done any work to it recently. any suggestions on what to use for smoke? anything i can get at cvs?

 

My first thought was the fast idle valve since he didn't mention that his car stalled. From what I know, most vaccum leaks tend to have your car stall. But, I'm not too sure, look for a leak first, then look at you throttle.

 

Actually, how old is your car? If it's really old, then the possibilty of fast idle valve failure is higher. Since you have a stock unmodified car it's really hard to track down the source of the problem.

For now you can try closing the idle control screw as much as you can. It's on the throttle body above the intake area and looks like a bronze slot head screw that's inset into the body.

Small vacuum leaks do exactly what he's talking about. I see it all the time when there's lots of mods to the intake area or vacuum line changes. I had a bored throttle body for about 3 months that would not seal properly unless you snapped the throttle shut. Nearly drove me insane, high idle and bouncing idle. I also had it when the nylon line on my autometer boost gauge cracked. Took me forever to figure that one out.