Hey y'all its a 89 xj with the 4.0. Its got 208,xxxish miles on the motor. Lately its been starting with a high rpm in the 2000 range for about 4-5 seconds and then when it goes back down it will idle kinda rough. Only mods to engine is intake and exhaust. I run shell 89 and the occasional Lucas fuel injector cleaner. So it shouldn't be about bad gas. I have always ran shell 89 and nothing else goes in that motor. Wanting to maybe get some hints here before I start tearing into it and replacing parts!! Any ideas or if this happened to you also throw me a bone here. And let me know what you did to correct the issue. Thanks fellas. Also cruising at highway speeds seemed to sputter. Rpms bounced a couple hundred

 

is it the original fuel pump? whats your pressure like?

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id check pressure on fuel pump. and if uve never replaced fuel filter id throw new one on there take the coil off as well and have it checked at auto parts store to see if its putting out the proper voltage

 

also check the TPS sensor (Throttle Position Sensor) cause that will cause high idle as well.

 

start simple then work up to other things ,has the iac ever been cleaned ?????????????

 

Not sure if its the original fuel pump, owned the Jeep for about a year. Has a 4 month old fuel filter and problem just recently started. I have not cleaned the iac but is in the plans for tomorrow. Thanks for the info any more insight would be appreciated. Thanks

 

Moved to OEM tech since its OEM parts....

 

I did an iac/throttle body cleanup yesterday but it didn't do much because I've run so much injector cleaner in it that it wasn't that dirty. TB had some buildup, but not enough apparently lol. Definitely check those, however.