Replacing idler pulley, 99 E430

[pwells]

Car is a 99 E430, 90,000 miles.

There's an occasional washing machine noise coming from the front of the engine, thought it was either the water pump or power steering. It got worse today so I took another look and can see that the serpentine tensioner pulley is wobbling. Took of the belt and there's way too much play.

Doesn't look like a big deal to replace - if one of you out there has done this before I'd appreciate any tips.

thanks in advance,

Peter