why does my car idle poorly with the ac on?


Asked by Apr 24, 2015 at 09:36 AM about the 2002 Mitsubishi Lancer ES

Question type: Maintenance & Repair

when ever i turn on my AC the RPM goes down and cause the AC to not run properly and
the car to idle poorly

11 Answers


If you have engine light on,have it checked,but it sound,s like it may be the throttle position sensor bad,it controls the idle under load.

2 out of 2 people think this is helpful.

there are no check engine lights and i tried a couple throttle body sensors but the problem is the same.the car runs smoothly when ever the air is on but as soon as i turn on cold air the car starts to vibrate n the RPM goes down but if im driving the AC works good and as long as my foot is on the gas but if i remove my foot the rough idle starts

3 out of 3 people think this is helpful.

Have you had the throttle body and idle air control valve cleaned lately,dirty throttle plate will cause this.


i had a mechanic clean it but im not sure if it was done properly tho so im going to try that once more today and see how it works


know any thing else i could try if that dont work? and the radiator in the car dont look like it was mad for it do you think that could be causing it?


There is a relay that is supposed to kick up idle rpm when A/c is turned on

2 out of 2 people think this is helpful.

what is that part called and how do i fix it?


Best bet is your owners manual. I can download manuals for most all cars except Mitsu. You have to register with a VIN. Or it may be labeled in under hood fuse box, a relay not a fuse

2 out of 2 people think this is helpful.

ok thanks for the info

1 out of 1 people think this is helpful.

Good Luck. Hope you get it.

Hi I just recently replaced the PC on my lancer Mitsubishi 2005 2.0 question is do i need to reprogram it to the car?? My key don't have a chip

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