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Erratic Idle

Gonepostal

NAXJA Forum User
Location
WY
OK here is the issue. I have 98 with a stock 4.0 that runs good at highway speed after warm up. Prior to reaching running temperature the engine runs rough and lurches at low speeds. The engine seems to still not quite idle right after warm up but does run better. No codes are getting set so I have not been able to trace the problem that way. Any suggestions?
 
Gotta start with tuneup hardware. Fresh Champion copper plugs gapped to .035, new plug wires, distributor cap and rotor.

Sorry, should have included that I have already done this and checked for vacuum leaks.
 
Throttle Position Sensor is my vote, after all the easy, cheap stuff in ruled out. My '96 idled erratically, surged while stopped in traffic, dropped in and out of lockup at highway speeds. The best results were from OEM units from the junk yard. You can get a few for the price of one new one. Look around on this forum for the directions to test yours.
 
Double check that the throttle body bolts are snug and do the same on the intake manifold.
 
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