the 16vs are CIS, not regular EFI, your ECU does not control fuel output like later EFI vws. your fuel pressure regulator is built in to your mechanical fuel distributor and is possible that it is bad. i've seen it before, had the same kinda problem in the 16v that i used to have, replaced the fuel distributor and it was fine. kind of expensive though so do some more research before you go spending money. hope that helps