Aside from the usual (check the oil level and colour/consistency, check for engine and gear oil leaks, see how it starts up - cold, check if it blows smoke from the tailpipe, check the gearshift quality, does the clutch slip, clicking sounds from the CV joints, tyre treads, etc):
Air conditioning - check if the compressor is noisy and how long it takes for the air to turn cold. Any longer than 30 seconds is not good. My compressor failed recently, cost around $900 for my local air con specialist to replace.
If it has power windows - check that they all go up and down fine (the clips that hold the window glass to the mechanism always break eventually, and the glass falls into the door - very very common with Mk4s). This is a major pain. My drivers door window mechanism broke a few months after I bought my GTI. I'd recommend getting some repair kits from the UK just in case.
Check that the door locks all work, as it's very common for the solder joints inside the lock module to fatigue and crack.
Ride quality (condition of the struts and bushes). Suspension noises, knocking, etc. Worn out bushes on the front control arms and rear axle beam, creaking on full steering lock indicates worn out strut-top bearings, none of these things are unusual from what I've heard.
I only have experience with the 1.8T so I can't comment on a 2.0, engine-wise.
Bookmarks