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Idle Issues

cmeuzelaar

NAXJA Forum User
Location
Madison, WI
Help!

OK, you've been great with advice so far, so here goes another one for you: my '89 XJ 4.0L w/ 240k on it now likes to idle between 1750 and 2000 RPM (unloaded) once it gets warm (after I've driven it--it may climb there if I just let it sit and idle, but I've never had the time to check). Sometimes killing it, letting it sit for a minute or so, and starting it again gets the idle back to ~1000 RPM, but not always. My TPS looks good (I only have a digital meter, so...). I have no idea how old it is (I acquired the jeep ~2 years ago and haven't changed it myself), but suspect it's the problem. Adding to the entertainment is that occasionally it starts and idles at ~300 RPM (yeah--it won't stay running in gear without gas at a stop). Finally, it appears that I have no "high idle" setting when starting cold (starts at about 750 RPM).

Are there other sensors that die commonly that I should be replacing as long as I'm going to do this? I am already replacing the Oil Pressure Sender (>120 PSI Oil Pressure reading most of the time).
 
The most common thing to cause a high idle problem is the TPS or connection from it to the engine controller.
 
Run a can of seafoam through the throttle body or use TB cleaning spray. The whole TB may be gummed up a little. May not solve all your probs. but I'd say TPS would be next.
Collin
 
my 89 4.0 had the exact same problem as yours. I just fixed it last week. Turned out to be a loose intake manifold bolt, towards the rear of the engine.
 
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