1990 Jeep Wrangler Engine Diesels and Runs On

Reader Question: I have a 1990 Jeep Wrangler that has started dieseling. We put a new engine in back in November (ourselves) and everything went fine.

However, with the dieseling I am beginning to wonder. When it does this, the gas pedal actually jumps/pumps and the throttle mechanism taps a few times pretty quickly.

Should we be looking at a throttle adjustment of some sort or would it more likely be a vacuum issue? We did replace the egr valve when we did the engine, and put on a new intake. With everything being moved around, etc.

I would not be surprised if some adjustments are off, but at this point we’re a little frustrated with even where to really start without spending more money on parts we may not need and/or taking it to the garage and spending a fortune just on diagnostics. Any ideas you could give us would be much appreciated.

Thank you,


Hi Elizabeth,

I am afraid I would really need to be there and look at this in person. It could just be that the base idle speed is set too high, or there is a problem with the idle speed control motor.

Usually dieseling is a result of the engine idle speed set too high, but most computer cars do not experience this problem because the computer is controlling the idle speed for the most part. Check the linkages, clean the throttle body of any carbon and dirt, and try to lower the base idle speed manually.

Austin Davis

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