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A/C causing rough idle & elec. problems


New Member
April 20, 2001
Reaction score
City, State
Southeastern, PA
Year, Model & Trim Level
2011 Hyundai Sonata GLS

My parents are having an odd problem with their '00 Mountaineer (4WD, 4.0LSOHC, 15K miles). Thought maybe someone could offer some ideas.

Occasionally while driving with the A/C (auto A/C) on, the truck's timing will start to flutter. It feels like you are driving on a rough road. As you come to a stop, the idle will drop to around 500 and the truck will feel like it wants to die. After about 15 or so seconds of stopping, the idle will even out slightly but still be about 600-650 or so. All of this only happens when the A/C is on and the engine is at full operating temperature. The dealer could not reproduce the problem, but replaced the MAF sensor under warranty. It didn't solve the problem.

Similarly, we noticed that the automatic headlights did not come on when we pulled into the garage today (my Mom had me drive the truck yesterday to see if I could reproduce the idle problem). Normally the headlights will kick on when entering the garage. So, in an attempt to troubleshoot the lights I was going to shut the truck down and restart it. While the truck was still running, I started shutting off all of the accessories. As soon as I turned the A/C off, the auto headlights came on. Very odd...

Do you think it is possible the A/C is causing some sort of problem with the electrical system? It is obviously interfering with the auto headlights, but I am also thinking it is affecting the engine timing/idle problems as well. It is just interesting the problems don't surface when the A/C isn't being used.

Thanks for your help!


I Drive By Brail
Moderator Emeritus
February 18, 1999
Reaction score
City, State
Montrose, CO
Year, Model & Trim Level
'95 Bronco '80 Toy
It sounds to me like a good possibility that there is some kind of electrical problem related to the A/C control system. If the turck is still under warranty I would take it back to the dealer and show the service writer exactly what you found. If they still claim that they can't locate the problem try another dealership. I haven't done much work on the newer X's and Mounts, yet (most are still under warranty) so I can't realy help much.


Elite Explorer
November 25, 1999
Reaction score
City, State
Allendale, MI
Year, Model & Trim Level
2001 Eddie Bauer V-8 AWD
Ity soulds to me to be unrelated. The headlights take a few mins to come on. they don't come on instantly because then if you drive thru a shady area or a bridge or the like, everyone's headlights would go on and off and stuff. I think your problem is strictly the A/C not cycling as it should. The compressor should go on and off so as to not make the engine die. Mine does anyway...open the hood and let it idle. watch the A/C compressor to see if it cycles. If thats not the problerm just bring it in under warentere.


Well-Known Member
November 19, 1999
Reaction score
City, State
Brewster, NY
Year, Model & Trim Level
1999 XLS
You may have a problem with the Idle Air Control valve. That is what is supposed to kick up RPM's when the A/C causes a drag on the engine. Sounds to me like it is not doing it. Search for IAC.... There are many threads regarding this item.

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