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Rough Idle

Brian82

NAXJA Forum User
Location
New Jersey
98 Xj, rough idling. Smooth off of idle, but idles rough. Common issues besides normal tune-up. I was thinking IAC , didn't wanna just through money at it. Common issues with rough idling? Again, its smooth accelerating, just idling at a red light or stop sign. Im thinking this is just a tell tail sign of a bad/ old, dirty Iac valve? no?
 
Jeep details ?? Engine, transmission, other basic info that applies ?

Is this a new symptom ? Try a bottle of fuel injector cleaner in the next two fill-ups. Clean the throttle body and idle air controller. Test the fuel pressure. Test the fuel injectors. Inspect the engine and transmission mounts.

The Jeep 4.0L has never been known for its smooth idle, age and miles do not improve the idle. If it isn't stalling at idle, it may not be a problem.
 
Jeep details ?? Engine, transmission, other basic info that applies ?

Is this a new symptom ? Try a bottle of fuel injector cleaner in the next two fill-ups. Clean the throttle body and idle air controller. Test the fuel pressure. Test the fuel injectors. Inspect the engine and transmission mounts.

The Jeep 4.0L has never been known for its smooth idle, age and miles do not improve the idle. If it isn't stalling at idle, it may not be a problem.

its a 4.0 with the auto aw4 trans. ive owned several 4.0s, never had one idle like this. im use to there "normal" idle. Wasn't sure if this was just a positive tell tail common issue with iac. I do need to tune it up.
 
The computer only manipulates the IAC when vehicle speed is below 20 mph (trans output speed) and foot is off the gas (throttle position sensor). IAC is most likely. You can clean it pretty easily. A good idea to check vacuum too, you can get a test gauge from autozone for $15ish. Sometimes the paper gaskets around the throttle body get brittle and crack. There's also a small gasket around the IAC housing on the throttle body that goes bad, not available to my knowledge, have to use RTV to make your own gasket. Another thing worth checking is the TPS itself can go bad and cause the computer to do weird things (like turn IAC off when its supposed to be on), but that is money
 
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