Vibration at idle, in gear
 

I have a vibration at idle when in gear. It's worse with the AC on. It also seems more prevlent once the engine warms up. It goes away when the idle hits 525 RPM. Sometimes it goes away by just turning the AC off. Also, I had the alternator replaced about 1500 miles ago. I had the vibration prior to the alternator being replaced. I have done a search, but haven't found a post with quite the same symptoms.

2002
A4 Coupe
35,000 Miles

Thanks in advance.

check your belts & idler assy. (tensioner)

The idler was my first thought. I had the serpentine replaced with the alternator.

I guess the other question is should I replace both assy's while in there?

Same problem when brake pedal is depressed and I go into gear it happens, Reverse is more of a problem then drive. And AC does add to the problem. No issues when I am off of the brakes and rolling.

Good point. Mine does the same as soon as I get off the brake pedal

If you car's idle is at 525 rpm I am surprised it will idle at all. You would have a heck of a shake. I have a cammed LS1 that shakes some.:D Idle set at 850.

I did wonder if the idle is low. It idles at 500 with AC on

Normal Idle is 750+/- When you turn on AC your car's computer should bump the rpm up 50 rpm. If your tachometer is showing 525 on start up and 500 with AC, that is not right. Get a dealer, buddy with a HP tuner, Auto Zone dude etc. to bump up your idle speed to 750,,,bet that solvles your stated problem.


We will be waiting if it doesn't,,,,let us know!:thumbs:

Is the proper idle different between a M6 and an A4?

Bump

Same problem
 

I have exactly the same problem with vibration at idle in gear. RPMs are around 500 and I get a vibration. A local shop I use has changed the tentioner twice. It goes away for a day or two and then comes back.

Did anyone find a fix?

Thanks, Ron

I wondered about that low idle number myself. Thought it migh be a typo it was so low.

Question now is what is causing your idle to go so low.

Your idle speed is correct, check the pulley on your alternator it should be a clutch type if not that is your problem.:thumbs:

I dont have the low idle problem but I do have the problem with the squeaking/sqealing so im going to replace the belt, idler, and tensioner

Not sure if this will help or not, but you might want to check for the "harmonic balancer wobble" that these things are known for. It may not be the cause of your low idle vibration, but if it does "wobble" it can cause the belt to wear out and cause the squealing others have mentioned.

Thanks for the ideas. I'll check them out.

I had the alternator replaced about 1500 miles ago. I had this problem prior to having the alternator replaced. In other words, replacing the alternator did not fix the issue. I'll be getting the car out soon with the weather getting better and taking it in to see what the service people say.

clean your throttle body probablly idleing too low ? you know how these engines are about carbon buildup.

Well, sainthinds, my mechanic agrees with you. He'll be cleaning the throttle body tomorrow. I'll let you know if this turns out to be the solution.