Jeep 4.0L high idle when map sensor vaccum line connected.

[Eric]

Hi. I have a 1988 Jeep Comanche (renix non high output) that has a very high idle when the map sensor vacuum line is connected to the throttle body (where it should be). I don’t have a tachometer, but it sounds like it is 4-5k rpm.

When the map sensor vacuum line is not connected the idle is slightly high, but tolerable in park. When it’s in drive, the idle goes down even more.

Of course, the engine is burning extremely rich and getting terrible gas mileage with the map sensor getting no vacuum.

I’d rather not drive it until I figure out the map sensor issue.

I have replaced the throttle position sensor, idle air control valve, coolant temp sensor, o2 sensor, and map sensor. Throttle body has been cleaned as well. It also has a clean air filter.

The only other things that I could think of are seeing if the exhaust/intake manifold bolts are tight and getting new crank case ventilation valves.

I don’t see or hear any vacuum leaks.

Does anybody have any ideas?

Any help or advise would be appreciated.

Topic

[Chris]

It sounds like the issue you are having is a rich condition, not a lean one. If you have a fuel pressure regulator, test it to make sure it is working properly by disconnecting the vacuum line right after you run the car. If you see fuel, it is bad. You can also disconnect the line while the car is at idle and see if there is a change in idle. You could also test for leaking injectors. You can also check your o2 sensors to make sure they aren’t bad with a computer. Do these checks to diagnose. Don’t spend money on components you don’t need. If you can’t diagnose, go with the cheapest solution first. Good luck

[Author]

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