REALLY common problem on this car. Search the boards. There is a pressure accumulator near the fuel pumps that goes bad, check valves in the pumps, misadjusted air plate in the throttle body, bad pressure regulator, and finally the entire fuel distributor can leak down causing this. Best way to check is with a fuel pressure tester, I understand, and a knowledge of troubleshooting this problem. I never completely fixed it on the 87 300e that I had.
(Oh man, this car is sooooo fast.)