The high idle could be a result of many things. Might need a new idle control valve (or clean it out), possible vacuum leak somewhere. But the bucking is caused from either fuel delivery or ignition problem. I agree with MERCEDESTECH you should check out the ignition system top to bottom.
I think these cars can sense an over speed condition and then cut off the fuel. I believe that is done in the fuel pump relay. There might be some component that thinks it should shut off the fuel supply. I know that the fuel pump relay does have an input signal from the ignition unit which could be used for this purpose.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k