why does my car idle poorly with the ac on?

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.

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

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

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

ok thanks for the info

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

My lancer started idleing rough and accelerating poorly I checked spark,compression, and I was told it was an injector so I replaced them and still happening

Kewaine Have you fix the problem of the poor idle when AC is on I have the same problem Please let me know Thank you

@kewanie. If your throttle body is a "drive by wire" you have to reset the "learned values" from a OBD scanner after cleaning the throttle body. Same happened to me and after a reset everything back to normal.

Kewaine did you fix the idle problem when ac is turned on..please if anyone can help me.

I expect you're getting too much load on that wiring system. First I'd check for any wires on that circuit that are open. If a bundle of wires are rubbing on anything they can be rubbed bare. If your ground wire in that bundle is bare you'll get an overload and probably a blown fuse or defective relay. Check fuses. And relays. Clean intake valve (car off, negative battery terminal off),spray proper cleaner into valve, wipe paying attention to the edges. Dry as much as you can with cloth. Do same for throttle control. Wait 30mins for fumes to evaporate and all is completely dry. Check air filter as a clogged one puts more load on the valve and check for air leaks along your air line, especially at the joints. Then try again. With AC off. Rev up or drive around for a few minutes for computer to reset. Then Let it sit, off, for a few mins. Try again. The computer needs time to reset itself and sometimes that takes a few days of driving. Idle speed when the engine is warm should be about 900rpm. As you probably know. I'm having a hard time setting my computer since I just put in a new battery. But I'm going to clean my valves before I do anything else. It is idling just a bit low, but not rough, when the engine is warm. But in your case it does seem like an overload on the electricals so check those fuses and relays. Mitsubishi manual is about as useful and IKEA instructions!! I use YouTube and online sources. Much better info. Hope this helps. Look for those wires rubbing and fix them asap. A bad ground wire will blow a fuse and stall your car whenever another load is applied, like your ac. I wouldn't even try putting on the AC until you've reset your computer. I drive for 10 or 15 mins. Park. Do again. 3 times. Then try with the AC. Hope it helps

Also the manual makes zero mention of relays!! Zippo! So it's hard to find the right one. They are not fuses. They provide power to the fuses. But if you don't know which one it is (they are the bigger black and sometimes colored units in the fuse box). They are inexpensive and worth a try if you haven't resolved the problem otherwise