Try checking your timing. These motors seem to come out of timing sometimes, it should be at 6 degrees at the very least. 8 should be no problem, unless you are running your car on apple juice/
I also recommend servicing the throttle body as well. Remove it right from the car and clean it thoroughly with mineral spirits. cis is very sensitive to gummed up t bodies.
To properly tune cis tho, it's best to have a co meter, but some people are really good at using there ears and nose while messing with the mixture (3 mm allen key I think....)
If you just type in 'how to adjust cis mixture on an 8v 1.8 vw' into google or the like, I'm sure you will find the answer there and if all that fails, then why not throw on a carb? It's all the rage!
Oh and do you have a Bently's yet? That will help alot. Great book!