Hi
I used to have similar problems with my mk2 16v sometimes it was a complete pain to start and you had to keep it on the starter for about 20seconds. I also experienced it stalling at junctions and it would generally be gutless until properly warmed-up.
If you were only experiencing starting problems I would suspect the cold-start valve. This valve is like a fifth injector which only operates for the first few seconds when the key is turned from cold (thus enrichening the mixture as a choke would in a carburettor system).
As you are having problems during the whole warm-up phase I would suspect the warm-up regulator (this can be found on the right-hand side of the block with a couple of fuel lines and an electrical connector).
This regulator lowers the fuel pressure during the warm-up phase. This in turn allow the air flow meter to rise easier which in turn allows more fuel to flow (again enrichening the mixture). The proper way to test the warm-up regulator would be to put a pressure gauge in your fuel line and see that the fuel pressure starts off low and rises as the engine warms up.
A new regulator is about ?80 and isn't a bad diy job.
Unfortunately I wrote my 16v off before I got round to replacing the regulator so I can't guarantee that this will solve the problem.
http://www.auto-solve.com/mech_inj.htmI found this site very useful for understanding the fuel system.
Hope this helps
Toby
