There is a breather pipe that goes on these that causes rough running. It is at the front of the block behind the inlet manifold and runs from left to right.

Check it and also check where it terminates for perishing splits etc. before you condem the engine.

We (the Wife) had a 1998 MK1 1.6 that had done about 150k miles with no issues. It did have that breather pipe issue and was a bit doggy for a while until I changed it but after it was fine for years and many more miles.