'82 1600 cabrio GTI stutter

Hi, my cabrio' has just developed a stutter under acceleration which is more noticeable under light/normal acceleration than heavy acceleration and only seems to be around the 1500 - 2500 RPM range, particularly in 1st, 2nd and third gears. Can anybody help please?
Cheers, Siggy.

This has now got a lot worse and there is a constant stutter or shudder under load in all gears mainly below 3000 RPM, which almost feels like you are driving on out of balance wheels until you decelerate and it's all smooth again. I'm wondering if the airflow sensor or the fuel filter could cause this?
Thanks in advance, Simon.  (desperate newbie) :dontknow:

sounds a bit like a missfire, when was it last serviced?

only 12 months ago, but I don't think the leads were changed.

What is the condition of the fuel filler neck ?