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Discussion Starter #1
i noticed this morning that when i turn the heater to high the idle goes up and when i turn it off it goes back down i have a 1999 jeep wrangler tj.
 

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Full Size Jeep Dr.
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3,424 Posts
Heater, or heater/defrost, or defrost? If you've got heater/defrost or defrost selected the AC compressor will run and that will cause the idle to change slightly.

It's also possible that the compressor runs intermittently on just the heater setting too. I haven't dug into the HVAC controls on TJs.
 

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Full Size Jeep Dr.
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That's normal. The compressor runs to pull moisture out of the cabin. That's what fogs the windshield/windows.
 

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This will especially happen if your engine is the 2.5L. It has a special circuit to raise the engine RPMs when the a/c compressor is turned on.
 
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