Ricky,
I had a similar experience w/my 107 (an Aug. 1989 300SL in the UK - sadly never supplied to the US market). Try replacing the gas pump relay (a black box with connectors) which is situated behind a pop-off cover inside and at the back of the glove box. They're expensive and my MB dealer let me switch it over at the dealership, in case it didn't work. Et Voila! it's been as good as gold since. One word of advice; MB "moved" these relays around from model to model and sometimes year-to-year (so I was told!) but start looking in that place first. Let me know how you get on.
Good luck!
Pete S

300 SL
230 TE
E320