Hi,

I'm new both to this car (been running nicely for the 3 months I've had it) and to fixing cars in general. Recap of the problem:

- Car was warm, running for an hour or so. Stopped at a red light in neutral and when it dropped to normal idle RPM it suddenly surged by itself, like the throttle was wide open. Tapping the gas pedal lightly once dropped it down to idle again, but as soon as it hit the 750 or so it normally runs at it, it immediately surged back up. Pulled over right away and had to tow it home.

- Since then it's stopped dropping to idle, just starts right up at high RPM (~3000ish?) and tapping the gas/throttle doesn't bring it back down, though it doesn't go up as high as it did when it first started happening. (I haven't dared run the engine long enough like that to see if it tries to drop back down again after warming up).

- I've read a bunch of the posts on this forum and it sounds like possibly a dirty/bad IAC. My friend and I pulled it out and flushed the valve with brake cleaner -- came out pretty dirty at first, but eventually got it seeming pretty clean. Attached it and turned key to on and no response/click/movement on the IAC, which we read may indicate a bad valve (or faulty contact).

- We reinstalled it and tried bypassing it by disconnecting the IAC hose from the intake hose and plugging both openings -- plenty of suction, but it basically didn't want to start, just sputtered and died.

Does this sound like a good case for a new IAC? I'm trying to decide whether to go ahead and shell out the $150-200 for that part or if I should check more things first.

Thanks...

 

more likely a gummed up throttle body. the IAC can't let in enough air for 3000 rpm, maybe 1500, max, if it was jammed wide open.

do make sure your throttle cable isn't mechanically binding, you can do this by having someone repeatedly smoothly step on the gas and release it while you examine the throttle mechanism under the hood.

 

Seriously doubt the cause is the Idle Valve. I'd look at linkage first, then an air leak (suction).

 

It might be a misaligned throttle position sensor or the idle screw.

I had this happen to me once after I was fiddling with the idle screw on the throttle body to fix a low idle issue. At least I thought it was the idle screw, but it was the throttle plate rest screw. I had snapped the screw earlier, but it was still in the throttle body and it idled fine when parked and low speed so I didn't bother readjusting. The first time out on a road with a 45 MPH speed limit, though, the idle surged high and wouldn't come back down. I pulled over to a parking lot and was able to get the idle back down by manually revving the engine at the throttle body. The solution didn't last and it idled high again on the way home.

Since I broke the screw I had to readjust it down with pliers and put some blue Loctite on there to keep it from coming up again. I haven't had the issue anymore. What I'm thinking happened was the screw was backed out enough to keep the throttle plate from resting all the way so the throttle position sensor sensed that the throttle was cracked open slightly. I guess with the throttle not in the resting position, the IAC is disabled so the computer is just adding gas to compensate for the amount of air coming in.