I've searched but haven't found a similar problem. 1999.5 A4, 1.8T, FWD, 120,000 miles, bought used 6 mo ago, No mods except Greddy exhaust. Intermittent strong vibrations felt through the gas pedal, clutch pedal, shifter, and even rattles the dash sometimes. Idle is smooth and no CEL or codes with an OBDII tester. Did have a PO422 a couple times that may have been from bad gas - I know I had a bad tankfull about that time. Cleared the code a couple times, replaced the filter and ran Seafoam, and code hasn't returned. Inside of CAT looks clean and open, pretty lean looking, but that may be normal? Vibrations/resonance strongest 2500rpm up, and feels like the engine is going to shake itself apart at 5000. May last for 5 minutes or 30 minutes, then it will (mostly) go away. Engine will feel pretty smooth and normal. Definite improvement anyway - it still probably vibrates more than original but it is noticably smoother at that points. May stay smooth for an hour, and then the vibrations will return. They can be felt while driving, and while sitting still and reving the engine. Makes no difference whether clutch is in our out (seems to eliminate trans/diff). This seemed to begin a couple months ago, very minor, and has grown to being pretty constant. I have examined all motor mounts, moved the front snubber around, taken the exhaust on and off to make sure it wasn't in a bind (even tried the original back on there), and wiggled and prodded everything I can think of. The fact that it comes and goes, gets better and worse, seems to eliminate internal motor issues (rod bearing or something). One other item - it occasionally "jolts" or jumps when crusing, like the key was turned off and on for a microsecond, or even like the A/C compressor kicking in, but the A/C is definitely not on. Not sure if this is separate issue or normal.
No noises - other than the buzzing from the vibrations. I am going to pull the drive belt to eliminate the alternator/ps pump/water pump for a test. I was going to pull the exhaust off to test, but that doesn't seem like it would come and go.

Any thoughts? I've gone from loving this car to hating to drive it. Appreciate any suggestions.
Dave Jones

 

Have you inspected the main front-rear driveshaft (or others) for a worn U-joint? Also, how about your inner CV joints? That'd be worth a look too. Even tires out of balance enough may appear to be the type of problem you're seeing - if they shake the car badly enough, they might make you think it's something to do with the hard parts of the drivetrain.

 

This is an engine-related vibration, affected by rpm, not gear or speed. Vibration can be mostly duplicated sitting in the driveway. May be slightly worse under load, but that may be just all the other associated vibrations from the road.

Most logical suggestion so far has been the dual mass flywheel? I've searched and haven't found the same experience anywhere. The idea was that the flywheel is shifting around, throwing the engine more and less out of balance, leading to the feeling of more and less vibration at different times. Any thoughts or experiences?
Dave

 

Have you checked the vibration damper on the front of the crankshaft? I found mine with three of the eight screws remaining, it had almost came off, close one. I have a 2.8 which has 8 screws, your 1.8, according to the manual,has 4 screws.If the screws (special bolts and must be replace everytime they areremoved)are loose use 242 locktite and torque to 7.5lb.+ 90'(1/4 turn), from the manual.Hopefully that is it as the flywheel is a lot more expensive.As it is fwd there is no driveshaft to the rear. B.