Fluctuating rpm at idle after exhaust manifold install
#16
CF Veteran
Your 99 does not have a sensor near the back of the head. Any leak before the throttle body is irrelevant..you can undo the 3 inch hose on your airbox and the engine will never know..any leak that varies idle speeds must come from downstream of the actual throttle plate or be a computer controlled variation
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jessethejeep (01-23-2021)
#17
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Year: 1999
Model: Cherokee (XJ)
Engine: 4.0L
tried checking for vacuum leaks again and still can't find anything. i have no idea what's causing the rough idle lol.
#18
CF Veteran
Ok, assuming your manifolds are not the cause and already did tune up, cleaned IAC, adjusted throttle cable, replaced TPS....
Next step would be cleaning throttle body, especially where plate sits, measure TPS output to verify its correct position at idle.
(CPS and Cam are a possibility too, since they are involved in engine running management, although I think they would be less likely with your symptoms)
Next step would be cleaning throttle body, especially where plate sits, measure TPS output to verify its correct position at idle.
(CPS and Cam are a possibility too, since they are involved in engine running management, although I think they would be less likely with your symptoms)
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jessethejeep (01-27-2021)
#19
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Bad exhaust manifold? I recently had a Dorman exhaust manifold that was welded very poorly internally and caused uneven and poor airflow. Just a thought.
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jessethejeep (01-27-2021)
#20
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Year: 1999
Model: Cherokee (XJ)
Engine: 4.0L
Ok, assuming your manifolds are not the cause and already did tune up, cleaned IAC, adjusted throttle cable, replaced TPS....
Next step would be cleaning throttle body, especially where plate sits, measure TPS output to verify its correct position at idle.
(CPS and Cam are a possibility too, since they are involved in engine running management, although I think they would be less likely with your symptoms)
Next step would be cleaning throttle body, especially where plate sits, measure TPS output to verify its correct position at idle.
(CPS and Cam are a possibility too, since they are involved in engine running management, although I think they would be less likely with your symptoms)
how can I measure TPS output? with a multimeter?
thanks for the help!
#21
CF Veteran
Yep
Can't access the notes I saved somewhere, but if you do a search on the TPS testing procedure, you will find it for sure.
Can't access the notes I saved somewhere, but if you do a search on the TPS testing procedure, you will find it for sure.
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jessethejeep (01-30-2021)
#22
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Year: 1999
Model: Cherokee (XJ)
Engine: 4.0L
SOLVED: turned out to be the upstream O2 sensor. put in a new NTK one and the problem is fixed. thanks to everyone for the advice!
#23
CF Veteran
Glad you fixed it
How did you come to find the O2 being the cause?
Thanks for getting back to the thread
Closure is good
How did you come to find the O2 being the cause?
Thanks for getting back to the thread
Closure is good
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