I have had a very similar issue, on my 1997 GTV TS phase 1. ( 110K miles)
I went to the expense of taking it to a local garage who said it " ...may be a blocked/faulty injector in position 4" , so with that in mind I purchased some second hand injectors (as the car is in daily use) and have had them refurbished at this place in the states.
Injector Cleaning Steps
(By the way, for anybody considering refurbishing there injectors I highly recommend this service. A 2 week turn around period from shipment to delivery or for about 60 quid ). I also received a breakdown of the valves operation pre and post service, and he confirms these are now in great shape.( He also returned the parts he replaced with new.)
I have since installed the 4 refurbished injectors however it still stutters arond the 2000rpm range...I notice more so when warm as oppose to cold engine temp, but my petrol consumption has improved considerably
So far I have eliminated:
Injectors ( refrubished installed)
Lambda ( new one installed last month)
Air intake hose ( new one installed 4 months a go)
Variator replaced and timing belt and air filter replaced recently.
So Im looking forward to any more suggestions......