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  1. #1

    Default Engine has a Uniform Fluctuation in RPM

    When I run my engine in park at lightly high RPM it has a regular fluctuation, it does the same at idle but not so regular. I installed a new EGR and EGR valve, I checked the MAP, IAC, TPS and their good. The O2S didnt check out, could it cause this? What else should I check?
    I have a '90 GMC Sierra with a 5.7 TBI with a automatic tranny.

  2. #2


    it is possibly for the 02s to cause the slight variation but unlikely they are more for a "long term" adjustments in the sence that your generally not gonna notice the changes that they are making. now when you say fluctuation is it a miss fire/ the rpms are dropping slightly or are the rpms picking up slightly as in you might have a leaking injector on your tbi and its more noticable when your on the throttle a smidge because your pushing more gas at the injector so the drip coming from it is a little more. so determine if your r's are dropping then picking back up or picking up and then dropping back down then check the issue it leads your to.

    hockey is life everything else is a crutch

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