Difficult starting - 1993 190E 1.8L W201 - help !

[kepla]

Okay, the car is a 1993 RHD 1.8L 190E with only 20624 miles on the clock.
About 3 weeks before Christmas it became difficult to start if it had not been used for a few days, but fine when used everyday, and would not idle properly or accelerate without mis-firing untill it had a few high-speed miles. Then everything fine untill left for a couple of days again.
After being 'rested' over the Christmas break, it will now only start if churned over for maybe ten minutes while pumpng the throttle. Once started, it just falters and dies if I let the revs drop below 1500. Attempting to drive off is pretty much impossible - put it in gear and it just falters and stops (it is an auto trans).
Last weekend I managed to keep it running long enough to get up to 90C on the temp guage, but it would start hot any easier.
I've removed the air cleaner and checked that everything looks clean and not stuck. I also (with difficulty) checked the connections to the OVP relay (and tested the fuse) and the control boxes behind the battery.
I am now pretty much at a loss as to what to check next - the electrical controls for the mechanical fuel injection seem pretty complex and I could do with some guidance on how to ensure everything is working properly.
I would much rather use logic to discover where this problem lies, and not just start fitting expensive replacement parts willy-nilly if this is possible.
Anyone got any good ideas where to look next ? Not just what to look at, but where to find things and how to check them.