Causes for '85 500SEL "Hiccup/Hesitation"?
 

My grey market '85 500SEL has been doing something weird lately that it's never done before. While being driven, all of a sudden it feels as if the engine is going through a "hiccup", or is hesitating..or can't decide whether to rev up or down. At first I thought it was the transmission jumping between gears, but then I remembered the transmission on this car is rebuilt and has less than 10k miles on it.

She was sitting a while before I drove her, so I'm thinking maybe I should buy some octane booster and fuel injector cleaner (recommendations?) to see if it's something minor. But I don't feel comfortable driving her while this is going on.

Any ideas on what this could be, or what I should ask the mechanic to check for if I take her in? Thanks guys.

maybe,loose connections under hood,fuel filter,or fuel pump connections.