Question about 1998 GMC Sierra

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I have a 1998 GMC Sierra, 5.7 liter Vortec 4x4. It has 160k miles. I have noticed that it idles at around 500 rpms when its warmed up. Not sure if this is normal. However, I have noticed a bit more vibration from the motor right when i start it up. Also, as I'm accelerating, my rpms will fluctuate. Not so much at higher rpms, but as I gradually accelerate. I am leaning towards the EGR valve, but I really don't want to replace it if that's not the real problem. Any help in this matter would be appreciated.

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The normal idle for your engine should be 550 to 600 RPMS so thats not to far off . But the fluctuation is more likely the crank pisition sensor then the EGR valve this engine has a condution called crankshaft wip witch is normal but going down a rough road can somethimes set off a misfire code It wouldn't be a bad idea to take the EGR valve off and clean it and check it but the CPK would give you the fluctuation in RPMS . It still could be a few outer things but this it the most likely cause

Posted on Apr 02, 2011

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