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Jerry, Master Mechanic
Category: Audi
Satisfied Customers: 16826
Experience:  ASE Master, 30+ years exp. imports and domestic, former shop owner
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Audi A4 has severe vibration and shaking under acceleration,

Resolved Question:

Audi A4 has severe vibration and shaking under acceleration, off power car is smooth, what could be the problem?
Submitted: 7 years ago.
Category: Audi
Expert:  Jerry replied 7 years ago.
Hello and welcome to Just, Super mechanic here. About your vehicle.

What year is it?
Does it feel like the engine has a miss in it?
Customer: replied 7 years ago.
no miss at all, engine runs smoothly at idle, and revs smoothly...
Customer: replied 7 years ago.
and its a 2004
Expert:  Jerry replied 7 years ago.
There could be a problem with one of the inner CV joints. That will give a vibration when under an acceleration. Normally will feel like a second order type vibration. That is that the axle wobbles 2 times for each one revolution.

You would want to raise the vehicle up, (preferably on a lift) and spin the wheel(s) by hand and see if the axle moves up and down when you reverse the rotation of the wheel. As the inner part starts to turn, you may notice that the axle takes some time to start turning, (play in the CV joint)

More than likely there is only one that is bad, so you can compare each side to the other.

Unless, it is in the driveshaft itself, which would be more of a violent rumble that seems to become more less when you get up to a higher speed.
Customer: replied 7 years ago.
yea it's actually more like a violent rumble, so you do not thing it has anything to do with the catalytic converter? in the even that it is the drive shaft...would the entire shaft have to be replaced?
Expert:  Jerry replied 7 years ago.
There are normally shops that specialize in driveshaft work. They could possibly rebuild it if it is not bent. However, it is most times more cost effective to replace it with a good used one if there is one available.

The P0420 code is just that the catalytic converter is not cleaning up the exhaust gases as efficiently as it should, that wouldn't give any running problems, (or vibration) only a lack of power if it were to become clogged up.

Of course, you will want to be sure that the transmission mount is good and not allowing the driveshaft to sort of bounce wheile your driving.
Customer: replied 7 years ago.
one more question, so is it a possibility that it could also be the tranmission mounts that are bad? would that cause the rumble, and if it is the transmission mount would i still have to replace the driveshaft or do you think just changing the mounts could eliminate the problem?
Expert:  Jerry replied 7 years ago.
I fthe mount is allowing the trans to bounce up and down when under a load, that could be the whole problem. Normally you can spin the drivetrain while on the lift and see if the driveshaft is true. The trans mount could be checked by pushing up on the rear of the trans and see if it moves.
Jerry and other Audi Specialists are ready to help you
Customer: replied 7 years ago.
okay....sounds like that definetely could be the problem, one more thing, is it normal to see a little oil inside the hole that the ignition coil and spark plugs go into? if not what could be causing that?
Expert:  Jerry replied 7 years ago.
The valve cover gasket has a part in the middle that should seal up the spark plug holes. That is where the oil gets into the holes. It shoudl really be rather dry in there. the oil settles around the plugs and can eventually seep into the combustion chambers.

You may want to replace the valve cover gasket to avoid any problems in the future with that.
Customer: replied 7 years ago.
would replacing the valve cover gasket solve that problem?
Expert:  Jerry replied 7 years ago.
Yes it would. (sorry, my pc was acting slow..I had to edit the post about that)

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