high rev

[carcrafter87]

Does anyone know why my 89 Mj 4.0 is revving up pretty high when i start it.(I don't have a tach so i can't tell you an exact rpm but its enough to make me cringe. it doesn't do it all the time. thanx guys.

[88pioneer]

possibly IAC

[jpnjim]

Mine does it when it doesn't start fast enough (long cranking time).

I figure the injectors put more gas in during the long crank, and a few seconds of higher RPM's are the result.

 

I've also had (Renix) XJ's that do this for 20-30 seconds, or more after starting, and that usually tells me to check out the idle air control (solenoid on the side of the throttle body).

 

They get gunked up & crappy, a good cleaning works wonders. :yes:

[1987Comanche]

It was a bad TPS on my '90

[carcrafter87]

i cleaned my throttle body and iac seemed to help a little, ill test my tps later on this week thanx guys

[ComancheKid45]

Check your Exhaust manifold bolts as well.....that has seemed 2 fix mine for the time being

[88pioneer]

Could also be a vacuum issue. My vac line for my MAP sensor broke and it idled a lot higher