Engine races to 5000 rpms
09-09-2017, 10:00 AM
#1
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Join Date: Apr 2015
Location: PA
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Year: 1998
Model: Cherokee
Engine: 4.0L
Engine races to 5000 rpms
I have a 98 cherokee with the 4.0l i replaced the engine and when i went to start it the engine races to 5000 rpms and stays there. I checked for leaks the intake manifold it tight against the gasket i made sure it was seated properly. The iac fuctions in the sense that the valve isnt stuck i cleaned the motor. When the engine is spiking to 5k rpms i hit the throttle to see if that does anything but it just increases to 6k and doesnt slow down. I have no idea what is going on and i really could use any help, thanks.
09-09-2017, 06:55 PM
#2
CF Veteran
The motor can only race like that if it is getting air. And in this case, quite a lot of it. It would have to be a large leak, a completely opened IAC, or the butterfly valve on the throttle bod is not closed properly at idle. Check the condition of your butterfly valve when the vehicle is off, and ensure that it is seated properly, and that the throttle cable is not maladjusted after the swap causing it to sit open a slight amount.
09-09-2017, 10:35 PM
#3
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Join Date: Apr 2015
Location: PA
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Year: 1998
Model: Cherokee
Engine: 4.0L
Update
Well after a TSP cleaning the valve i proceeded to take the intake maifold off to find that underneath it had gotten hung up on the guide pin, it wasnt until i removed the air box and stuck my head down there that i saw it, well i alligned the intake and torqued it down and all runs well, thanks to everyone for your help.
