Gti Killer

my s2 is running 195bhp its 1989 i have changed the head as the old one was spitting out water and changed all spark plugs to ngk and also changed dizzy cap and ht leads but im still having the problem which is that when i fist start the car fir the 1st time in the day it starts up straight away and idles fine and picks up fine with no problems and i have no problems when it gets to normal running temp the problems start when i turn the car off and go to start it back up again, It starts to miss fire and spits and struggles to pick up revs but turbo still spins but when i let off of the accelerater the car idels at 300 rpm and the cuts out what could this be ive been told that it could be the esc (electronic spark control) has anyone had this problem before as its really starting to get me down now and im thinking of getting rid of it thanks for your help in advance