Hi, I was curious if anyone has this same problem with there Merc. I have a '90 300SEL with 75,000 Mi on it. When I burn Sunoco 94 octane all is well. As soon as I fall below that 94 I get a "stumble" at start up. This is brief but noticable. If I step on the fuel pedal while starting it is less of a problem. It almost acts like it is losing fuel prime but not sure that could be it. I was thinking new injectors but someone said they either work or don't. I have a new fuel filter and new wires and plugs about 4-5 years ago but not many miles on them. Anyone have any suggestions? I could put a new set of plugs in it, maybe Platinums and see if it helps. I believe something else is doing this. Look forward to any replys.