sporttruck88 Posted January 1, 2019 Share Posted January 1, 2019 I have an '88 MJ with a '90 4.0; when I start it up it idles fine but after I've driven it a while, the idle gets as high as 1600 rpm. If I shut it off and and restart it the idle goes back to normal but goes back up again after driving. Any thoughts? Link to comment Share on other sites More sharing options...
cruiser54 Posted January 1, 2019 Share Posted January 1, 2019 Have you ever visited my website? I would suggest completing Tips 1 through 5 before doing anything else. Link to comment Share on other sites More sharing options...
RangerDB Posted March 5, 2019 Share Posted March 5, 2019 And if 1 to 5 don't work, I'd try #11, it cured my idle problem. Link to comment Share on other sites More sharing options...
sporttruck88 Posted June 8, 2022 Author Share Posted June 8, 2022 Turns out it was the brake booster. Link to comment Share on other sites More sharing options...
cruiser54 Posted June 8, 2022 Share Posted June 8, 2022 Still oughta complete those Tips. Link to comment Share on other sites More sharing options...
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