I have an 04 A4 1.8T FWD, lowered at 50K with 18" wheels, new Pirelli tires. The car now has 197K and has just recently developed a bad vibration on acceleration.

I changed the CV assembly (with aftermarket parts)-no change so I put the old back on.
I changed motor and transmission mounts-no change
I changed plugs, coils and coil wires-more power but no change.
I changed the timing belt kit-it was just due-no change

The car has more of a vibration than before when idling but nothing crazy.

The funny thing is that it doesn't vibrate the same each time .. when I'm driving at 110km and gradually increase speed it shakes and vibrates, when I let off it decreases the vibration by 90% but a little is still there.

Sometimes I can step into hard and go through the gears with only a minimal feel of vibration but sometimes it is really thumping.

I'm stumped!

 

Do a compression test on the cylinders. They should all be the same or close. Sounds like you might be misfiring.

 

Thanks I'll do that.

 

All in the 170's