Could you elaborate what engine issues you started to see please and which tune? Stage 2? Who was the tuner? etcI tuned my mk3 rs basically as soon as I got it thinking it'll be fine what's the worst that could happen. Then a year into ownership I started seeing engine issues mentioned on the forum. 1 guy had his car mapped and was rejected a warranty claim which made me nervous incase my engine decided to go. Not to long after ford held their hands up and started to recall cars. Mine had the recall done and after 3 years of ownership I sold the car. Within the first 1k miles of the 2nd owner the engine went at 29k miles and the new owner had to fork out and buy a new engine as I only had 3 years warranty and due to the car being modified. If I was to do it all again I'd have went with the ford approved mods fpm375. Not sure if the new mk4 st has any ford approved maps you's can run but if not then me personally I'd hold off and let someone else try it first.
I had a lucky escape with my car thankfully but at the same time it was **** for the next owner spending all that money for the engine to go not long after.