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Most of the time cars vibrate when you turn the A/C on, but mine is the other way around, when the AC is off the car has a lot of vibration, if I turn on the A/C it will stop vibrating, I already went to the mechanic, they used the scanner and they can't find anything. I just changed the spark plugs and no change.

This doesnt happen all the time but it does most of it, any suggestion of what should I check?

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3 Answers 3

You may need a new air filter... I have 60k on mine and just changed the air filter... The idle is lower and not a lot of vibs... I would have vibes when I stoped and when I was at 1500 rpm. I got a k&n air filter form autozone for about $53 and some change.

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It should cause a MIL, but it sounds like an idle-valve is not working properly. There are probably at least two idle valves on your car, one for heavy load operation (A/C, power steering, alternator, etc.), and the other is for A/C. They bump up the airflow to the engine to counteract the power drain that those accessories cause.

If the normal one(s) are defunct, the A/C idle valve is making up for it when engaged.

Otherwise, a bad motor mount (mentioned already) would cause bad vibrations at arbitrary RPMs (usually idle!), and this would not cause a MIL.

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can you tell me what a MIL is ? –  isJustMe Sep 24 '12 at 13:14
    
nevermind.. Malfunction indicator lamp yeah it doesn't lighted up –  isJustMe Sep 24 '12 at 15:16

All I can think of is that somehow, when the A/C compressor is engaged, that the extra torque on the belt driving is somehow reducing the vibration you would normally get when the compressor is engaged. Perhaps the clutch for the compressor pulley isn't disengaging properly when you turn the A/C off.

I would check (or have a mechanic check) the belt tensioner and belt tensioner pulley, the pulleys on the alternator and water pump, and the general status of your current belt(s). It's probably way too soon for a belt to be bad, but if you have an issue with any of the other pulleys you might have prematurely worn out your belt.

Engine vibration itself could also come from cracked or broken motor mounts and/or transmission mounts; you could have those checked as well. It's unlikely that those two issues are related.

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