97 Ford Explorer, 110,000 miles.

Over the past few months the Startup Speed has Revved up. It used to rev up to about 1200 RPM or so, then drop down to idle speed. Now it revs up to about 2500 to 2900 RPM for about 5 to 10 seconds before dropping to IDLE.

 

Does anyone have a suggestion on this problem? Please respond if you do, the problem hasn't gotten better or worse.

 

Could be a slow/lazy iac motor. Try this. Have the engine running, turn on the ac and turn the steering wheel. Does the engine rev up with these actions? Both of these tests will communicate to the pcm that there's a load being placed on the engine, the pcm will then command the IAC valve to open in increments and then close some once engine idle is smoothed out. If the engine response seems slow after putting these loads on it, it is probably your IAC valve. With a normally working IAC, you should barely be able to notice a difference in engine speed when loads are applied. The frustrating thing about diagnosing an IAC is that a mechanically stuck IAC won't trip the check engine light to give you a DTC. Also check out all the tubing from the air filter box up to the throttle body. If excess air is entering the intake stream after the maf sensor, you'll get a lean mixture and the pcm is taking a few moments to compensate for it by kicking the idle high. In most cases though, an air leak would trip a DTC and cause the check engine light to come on.

There's not a whole lot of information for me to guide you on what to do next. There are more things that could cause this problem, but the two I mentioned would be my first two checks. Take care of it quickly, whether or not you have to pay. Theres not much worse for an engine than to rev up like that on a cold/dry start. It takes a second or two for oil pressure to build up once started and having it rev to 2500 rpm at that time is going to do damage.

Good Luck

 

Thanks for the help. It cost me about $45.00 and about 10 minutes with a 10 mm socket with a 3 inch extension. As soon as the new one was installed, I started it up, and the problem was noticibly GONE!!!

Thanks Again,
Mark

 

yeppers those IAC can do funny things, I think I read once where theres like 250 differnt settings it has in just one of travel,,,,,,,,,,