my audi a4 eletric window driver side works when it wants?

i think your promblem are the two plastic carriers that are fixed to the glass at the bottom, these break and cause your problem.Part no. from audi 4BO 837 463.
You will need to take out the door subframe to do this job,make sure you mark the position of taper wedges with a marker pen befour you unbolt the 4 torq bolts.
when the subframe is out remove the window motor(3 screw)unbolt the screws that fix the glass to the carriers, remove the glass carefully, you then can replace the new carriers to the guides either side cliping them on the wire, fit the glass , then back on the door frame.Be careful not to damage the door mirror.
Whole job should take about 1 hour

Stephen Chamberlain
September 2010