These are bad plugs! (Excuse the hair on it, I pulled them out of the bin to take a piccy).

And as Thom said they're not right for the 16v. I used NGK BKUR6ET-10 for the ABF,. THis is taken from NKG's website.
GOLF MK2 (84-->91) 1.8 KR / 16 VALVE 85 –> 91 BCP7ET
GOLF MK2 (84-->91) 1.8 PL / 16 VALVE 10/85 –> 10/91 BKUR7ET
I always get my plugs on ebay. £10 gets you 4 brand new ones if you look well enough
