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Q: Idles high without accelerating

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My engine was replaced in my 2002 Safari, but I don't know if the mechanic used a 2002 used engine or newer one. When I accelerated from a stop I felt the idle gradually increase speed until it reached about 50 mph. And I didn’t even press on the gas pedal! When I stopped the car it idled down to normal until I took my foot off the brake. When it got to around 3 mph the idle started to increase again. I replaced the oxygen sensor on the passenger side and the idle air control valve. I was going to clean the EGR valve but couldn't find it. That’s why I think it might be a newer than 2002 engine. I’ve read in that 2003 and newer Safaris don't have an EGR valve. Can you help me with this problem? What should I do?

A: Hello. Thanks for writing in about your 200...

Hello. Thanks for writing in about your 2002 GMC Safari. There are several components that may be causing this problem. There could be a bad throttle position sensor, a throttle cable that is sticking, or a vacuum leak. All of these things may cause the idle to increase on its own. My suggestion would be to have a certified technician, like one from YourMechanic, complete an inspection of your rough idling issue in order to pinpoint the problem.

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