MJ Comanche Tech. Stock & Modified. MJ (86-92)
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Mj 4.0 high idle

Old 02-25-2018, 12:08 PM
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Location: NH
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Year: 1989
Model: Comanche
Engine: 4.0
Default Mj 4.0 high idle

Hey everyone I've daily'd my 89 4.0 mj 5 speed for 5 years with no issues, until last year it started to idle high as the temp increased. During cold start it idles normal (around 800 rpm) but as the temp increases so does the rpm (around 1500 rpm). I've cleaned the throttle body, replaced the throttle body position sensor, idle air control and the coolant temp sensor with no luck. Has anyone fixed a similar problem?
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Old 02-27-2018, 12:19 AM
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Year: 1999
Model: Cherokee(XJ)
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Did you properly adjust the tps when you installed a new one? Also, if you haven't done so yet. Check out cruisers mostly renix tips. They're always a good place to start when having any renix era issues.
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Old 02-27-2018, 07:59 PM
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Year: 1989
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Engine: 4.0L inline 6
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I had the same problem and did the same things you've already done (1989 4.0 XJ), assuming your tps is adjusted correctly.

My fast idle as the engine warmed was caused by loose manifold bolts.

The top ones are easy enough to check with a 9/16 box end wrench.
Lowers will be a socket on a 6" wobble extension.

There are many more causes and cures in cruisers info if it's not manifold bolts.
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