things to check: windows clips and regulators go bad (windows don't roll up and down well or not at all), door lock actuator (door doesn't lock), wheel bearings (hub/wheel play), suspension (strut mounts, control arm bushings, tie rods, ball joints worn), fuel pump leaking or long start, noisy lifters, flywheel chatter, oil leak from turbo and/or intercooler, clogged intake/egr, engine leaks (esp from head), excessive smoke upon cold start or hard acceleration, low power/limp mode under load, always have codes checked with vagcom. Not exhaustive, but some of the basics. Good luck.