Sticking 89 560 SEL Cruise Control.

Thanks for taking the time to read this. I have a 89 560 SEL with a sticking cruise control. Twice this baby has had me a little stressed having to pull over and turn the engine off after using the cruise control. Both times there seems to be a lag in the gas pedal before using the cruise control to accelerate. e.g. You press down on the gas pedal and nothing happens, you keep pressing down about 50% to the floor, then Bam, it takes of like a rocket. Now you get to the speed you want to be at real fast..cause it's a 560SEL (;= Next you put the cruise control on by just hitting the accel lever. Everthing is good here. Now I just want to accel a few miles an hour to get just to the legal limit. Press the accel lever again and this heard of horses is off like a runaway stampede... Wow there.... hit the brakes... Nothing happens, I slow down but as soon as I take my foot of the brakes this 560 is off and running again. I thank Mercedes for Damn good brakes and my strong right leg to bring this heard to a halt. I have given the linkages under the airfilter and the linkage to the cruise control box a spray with lube but am sorta not looking forward to using the Cruise anymore. Any-one heard/had this happen. p.s. one more question. What is the big round switch on the floor under the gas pedal for ? It was lose and flopping around down there. Now safe back in it's holder.