Having some weird vibrations while accelerating. Doesn't occur while coasting, idling, or if I stick my foot into it, but does occur when accelerating at a "normal" rate (in town going from 30 to 35 to 40). Also occasionally have issues starting that are solved by pressing hard on the gas pedal.

Thinking fuel filter or pump? Ideas, suggestions?

 

I had shuddering between 4-6k RPMs. It was due to the vacuum tube being disconnected from the actuator valve on the front of the manifold (ball-shaped thingy kind of hidden from view).

Re-connecting the vacuum tube fixed the problem.

 

+1

It's not the fuel filter. Check for vacuum issues.

 

Don't assume the starting problems and vibrations have a common cause. Can you tell where the vibration comes from? Assuming this is a Quattro, any chance it's coming from the drive shaft area?

 

From what I got in the short chat with my mechanic, it's likely either the tires (which have warped with high and low spots, have to got discuss this with other mechanic in town), the drive shaft, or something that isn't being seen when in the shop.

The vibration can be felt in the entire car, but is stronger in the front seats. Can definitely feel it in the throttle. Downshifting helps with the higher RPMs, but kills my gas mileage.

My gut was leaning towards fuel or something else since it only seems to vibrate/shudder when it's warmed up and it's less noticeable when I have less than 1/4 tank of fuel - thus the assumption that the start-up and vibration were related. Also not entirely sure of last time fuel filter was changed.

It is a 1999 2.8 Quattro, 183k miles.

 

Yea, tires are a possibility. Twice I've had friend's cars where we just could not track down a vibration, till we swapped out the tires. Belts can slip, then you might as well not be balanced at all.

 

+1

I just went through a similar (hair pulling) ordeal with a brand new set of tires. Even though they were brand new, they had radial pull, so I never considered them to be the cause of my severe pulling. until I finally had them rotated....after I exhausted every other possibility (including 3 alignments).

The minute I had them rotated, problem solved.

 

It might also be related to control arms or tie rod ends. It's not uncommon for the control arm or tie rod bushings/ball joints to fail and cause vibrations under load/acceleration.

Your mechanic should be able to know how to check for play in these areas. If there is any excessive movement from either I would replace suspected parts ASAP. A ball joint failure could be catastrophic and cause you to loose control of your vehicle.

Jason

 

My guess would be an axle. Inner joint, Did you say quattro? if so the center shaft can do it. do you feel it in the seat or the steering wheel?

 

Both good ideas.

If you want to check all 3 of our ideas at once, just take your car to somewhere that will give you a free alignment report (have them put it on the rack and give you a printout of what you need).

There are plenty of tire shops thet'll do that for you for free.