My mk1 is spluttering from 2000 to 4000 rpm . It pulls great anywhere else . Any suggestions where to start and what to try first would be great. Changed the air filter no difference was going to try fuel filter next .
Maybe a set of new leads; they can very quickly go bad after 50-60k
Get any fault codes read
As per AST, may be plug leads. I had same on my Mk1 a few years ago. You can test them individually using a multimeter (lots of YouTube vids) which is what I did and found one lead was bad. Replaced it with a used OEM one and everything running fine again.