gimik

stfa but no luck.. how long should stock motor/engine mounts last? how bout trans. mounts?

diagnosticator1

experienced during service.
The deleterious accumulative effects of ozone, high temperatures and contamination from oil leaks etc can cause failure at a relatively low mileage. Service life is also determined by mount design. Electrically controlled/hydraulic mounts are not as durable as a solid rubber type mounts.
Transmission mounts are not as heavily loaded and do not experience the same stresses in service that the engine mounts receive.
If the engine mounts need replacement, then the trans mounts should be replaced at the same time, to maintain correct drive train position and alignment.

Are you experiencing problems that are implicating the engine/trans mounts as needing replacement?

gimik

i'm not sure whether it's mounts or what, but i was trying to get an idea of what i can expect out of them given typical/average use conditions. (i'm at 94k miles)

diagnosticator1

does not identify one or more mounts as damaged, first try readjusting the front torque reaction snub mount bracket, and evaluate if that has any effect on the vibration problem.

First, loosen the engine and transmission mount bolts, just enough for the assembly to move on the mount pads if needed. Start the engine and allow to idle, trans in "P", for a few min on the loosend mounts, then with the engine idling, retighten the mount bolts starting from the trans mount then the opposite diagonal front engine mount, across the the other engine mount, and finally the diagonal opposite rear trans mount, last. The sequence will be in a "X" pattern. This is to confirm no static side loads in any of the mounts.
Now procede, again with the engine idling, in "D", ebrakes engaged and wheels blocked, adjust the position of the snub mount pocket bracket so that there is no torque reaction pressure on the snub mount, while at idle in "D".
Move the snub pocket as needed, then retighten the bolts before turning the engine off. Also, put the trans in P, then R, and then back to D, and evaluate the effect of the adjustment, a minor final additional adjustment may be needed.
To find the best idle speed for minumum vibration in "D", continue with the steps below.
Using a VAG-COM, with the engine fully warmed up, A/C in AUTO mode, open the engine electronics, and then go to adaption channel 01, click on the "Read" button. The view will show: Actual Idle Speed, Idle speed requested, in the first and second fields from the left, at the top.
Below that, there is the adaption value setting, try increasing the value by 1, say from "128" to "129". That will increase the idle speed 10 rpm. Note the relative idle quality while in "D", by varying the idle speed up 10, 20, 30, > up to 50 rpm and below 128 to 127 etc, in steps of 10 rpm. There will be an idle speed that results in minimum vibration while in "D". (My '03 Avant TIP idles best at ~820 RPM, your best idle speed may be a little higher or lower than that.)
Be sure the associated adaption value for the minimum vibration optimum idle speed is "saved" in channel 01, before closing the VAG-COM. Finally shut down the engine to store the new adaption value in the ECU.

If the above settings do not help, replace the mounts and then perform all the steps described above to optimize the new mounts as installed.