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Message: <blockquote data-quote="DarkNinjaSG" data-source="post: 23143" data-attributes="member: 12584">Hello!I have a 2000 Silverado 1500 with the 4.8 that has 140,000 miles on the engine. It’s been acting strange recently. If I drive it for over an hour at highway speeds or for over 30 minutes in stop and go traffic, the engine will start to idle at 1,000 RPM. If I shut the engine off and then immediately start it again it will still have a high idle, but if I shut off the engine and wait about 30 seconds and start it again it will drop back down to its normal idle (500-600 RPM). Also, during the high idle if I blip the throttle it will take over 10 seconds to drop back to idle. I have checked for vacuum leaks and have found none (checked intake manifold gaskets, PCV valve hose, all around the intake manifold, around the throttle body and IAC, and the intake tube and MAF sensor). I also cleaned the throttle body and IAC seat, but that doesn’t seem to have helped. I also checked the IAC and both coils read 52 ohms. I am stumped with this .Any help would be appreciated. Thanks!Edit: also, after waiting the 30 seconds and starting it again it almost stalled before catching itself and returning to a steady 500-600 RPM.</blockquote>