Gr8White

I bought a 1999.5 1.8T project with 128,000 miles and I noticed that when the car was idling in either park or neutral and without the air/heat on, it would run smooth, but then when I would put the car in gear or turn on the climate control, the car would vibrate so bad that you would hear a constant droning inside.

VCDS didn't indicate any codes and would not show any misfires. I started with the easy stuff, spark plugs and seafoam without any luck. Couldn't see anything wrong with the motor mounts but decided to replace them due to the age of the car. New motor mounts did not resolve my problem and after replacing the motor mounts, I am now hearing the droning vibration all the time!

My questions are why am I now hearing the vibration all the time (versus only when it was in gear or with the climate control on) and what could I be overlooking?

4bagels

Sometimes the snub mount can cause this. Sometimes realigning the snub mount can help. But sometimes a performance unit is too hard and vibrates all the time (go back to a softer or stock unit).

Gr8White

That would explain why the initial problem only occurred under load and why after replacing the mounts, it is doing it all the time. Any tips on getting the alignment correct; pressure up or down on the mount? Thanks.

4bagels

I've seen a few posts that describe the alignment procedure like this, but be careful since it has you use your hands and tools VERY close to moving pulleys/belts... Run the engine until it's at normal operating temperature. Shut off engine. From underneath, loosen, but don't remove, the nuts/bolts holding the snub mount bracket so that the bracket can move around. Go start engine. While the engine is idling, carefully tighten up the nuts/bolts. That's it, really only takes a few minutes to do.

That might help. If not, you might want to consider replacing the snub mount with a stock unit (or others might have suggestions on a performance unit that is soft enough not to make this drone/vibration).