A100 Fuel problems (Was A100 only runs when cold)

I'm still having trouble getting my Audi 100 (1988, UK, 2.0 5 cyl RT eng., K-Jetronic) to run reliably. And getting a bit fed up with it now! I originally described the problem as 'only runs when cold'. But further testing suggests 'packs up when warm' would be more accurate as it is very difficult to start from cold on the next attempt. Once started, it runs fine for about 15 mins, then the revs drop to about 100rpm for a few seconds before stopping. Generally you can not restart it. It's done this 6 times out of 7. I have tested the ignition system and everything checks out ok - I always get a spark. Cold start valve works fine. ISV responds to voltages. Removing the dipstick almost stalls it. Bypassing the fuel pump relay makes no difference. The fuel filter has done 7000 miles, and the pump has done 70,000 and runs quietly. When I can't get it to start, the plugs are dry so this suggests the fuel system is not working or something is telling it to shut off the fuel. What could it be?

I've read about the tank coating peeling issue - is this sufficient to stall a car? Apparently a solution is to cut the fuel pump screen. Is there a screen on both old and new type pumps - I can't see a screen on pictures of the old style pump

says this was fixed after VIN

44KN017651. Is 44ZJN248015 before or after this? If my tank is 2/3 full will I be able to get at the pump? (Still trying to get the guage sender out). When I release the fuel pressure at the warm-up valve there is always fuel there but it's only just worth getting a rag for. How much should come out? Are there any tests for the warm-up valve apart from the resistance (which is always 20ohms)? The Haynes talks about a fuel cut-off device on the airbox - the hole for it is blanked off on mine. Has another system replaced this? I've also read about a fuel pressure regulator attached to the fuel distributor but I've not got one of these either. What other switches or devices could cut off the fuel? Possibly something on the vacuum system? Can I get something to measure the fuel pressure? I've not seen this type of tool anywhere local.

Thanks for any help. Gary