[darkpuppet]

Changing the crank pulley with a UDP shouldn't hurt the driveability of your car, but it's possible that the alternator isn't producing much juice at idle.. not sure if it would cause driveability issues.

Someone with a bit more UDP experience may be able to provide more insight, but I don't see it causing issues.

What kind of driveability issues are you having? stumbles, stalling, poor reving?