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Funny idle behavior

I've noticed something strange with my 94 Suburban. Usually, right after a cold start, when I put it in gear (drive or reverse) and keep my foot on the brake, the motor will rev up and down - usually between

350-800 rpm. It cycles the idle like this every second or two. This is also noticeable when I take my foot off the brake to begin moving - like when I back out of my driveway. The vehicle will start moving, then start moving a little faster than expected, because of the idle surge. Even though it doesn't move that fast, it's a little disconcerting to be backing up, then feel the car speed up, even just a little bit.

This only lasts for less than a minute. After driving for even just a couple of dozen yards, the problem goes away. I've only noticed the problem when I start it after it's been sitting for an hour or more, and even then it's not guaranteed to happen every time.

Any ideas what might be the culprit? I'm trying to sell this car, and I'd like to have an explanation, or a reasonable fix, that I can give to a buyer.

Thanks in advance. Steve

Reply to
Steve Lewis
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It sounds like you have a vacuum leak. You should start the car and open the hood and listen for a sucking noise. If you can't hear one, you might use a spray bottle and just start spraying around the engine (almost randomly if you don't know what you're doing but particularly near gasketed areas of the intake or vacuum line connections). If you hear the idle increase when you squirt a particular area, try it again and see if you can pinpoint the place you're hitting and that will give you a good indication of a vacuum leak and where to find it.

-Bruce

Reply to
Bruce Chang

Could also be a malfunctioning IAC valve (sticky pintle) hunting for the right idle setting. First thing is to scan the PCM for diagnostic trouble codes.................to rule out an EFI component.

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Doc

Reply to
"Doc"

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