Hi Tom,
The idling can be many things.
I'm going to stick my neck out and say that everyone who seems to get this problem heads straight for the Idle Stabilisation Valve.
However, the component that we changed was an electrical component called Idle Stabilisation Control Unit or something similar. You'll need a Haynes manual but its found in the cabin in the centre console somewhere.
Find it, pull it and decide if the car is the same. If it is, then its dead. Your best bet is to find someone with a GTI and try theirs :-)
On the second subject about your car.
There are two possibilities.
Firstly, it is a Campaign and someone has put big bumpers on it. Find them, execute them.
Secondly, it is a 91 model with an E plate stuck on it. 91 models in 16v were available with optional extras such as 3 stripe interior, blacked out rear lights, and the original MK2 Campaign colours (graphite, blue, oak). And so for all intents and purposes, they look like a Campaign.
There are two ways to decide whether it is a Campaign.
Firstly the wheels. The 91 model had 15" rims which were similar to the Campaign, whilst Campaigns have 14". The wheels also have different number of spokes.
Secondly, ask your VW dealership for a print out of the main database showing your car. You will have definite proof then. 88 = Campaign, 91 <> Campaign.
I'd love to know where the number "50" came from?
Regards,
Justin Clements