i had an annoying problem similar to that when i had a S1 RS, it was traced back to the bottom boost hose being knackered. So when it came on boost the hose blew up like a balloon, caused me major headaches trying to find it & it was a pain in the arse to start aswell bcos it wld overfuel on startup and just flood.

have you maybe checked the wiring to the injectors?? they get very brittle eventually and if theyve been on / off a number of times in the past its poss the insulation may have cracked and it cld be earthing out???