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Discussion Starter · #1 ·
Any ideas on where to start looking for the cause of high idle? My 89 4.2 is idling at about 10k rpm.


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I assume yo mean 1K rpm. Hung up throttle linkage, high idle cam on the carb hanging up, Vacuum leaks will cause this too. Id start and see if your throttle linkage is hung up and if the carb throttle plate is closing all the way, that would be quickest and easiest. If you find nothing there have a good lok at the vac lines and yo can use a can of carb cleaner to shoot quick bursts of cleaner around to see if the idle speed is affected which would indicate a leak.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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^^^ What he said....

What Carb and emissions are you running? What are the temps outside lately

If its stock look extra close at the emissions vacuum lines.

If its aftermarket without all the emissions to be computer controlled, It could just be the actual engine temp. When my 4.2 warms up it tends to Idle a little faster than when cold after the choke opens up. Without a computer to monitor the rpms and adjust the carb, the engine temp and ambient intake air will affect your idle slightly just due to the fuel/air/temp mix
 

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Discussion Starter · #4 ·
Thanks guys. It looks like the stepper is preventing the throttle plate from closing.


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Stepper or choke cam? If its the choke you can dial back the coil (black round thing on side of carb). It may also be used up if its hanging up and you have a hard time starting when it cold.
 

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mine idles high too, mostly around 1500. Sometimes down to 1000. It will roll down to 750 and gets bumped back up to 1500 before too long.

Any ideas besides vacuum lines? Mine's a stock 4.2, one owner.
 
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