the wiring harnesses on this model (and many other mercedes) are notorious problem causers. i have seen the harness on the 600 throttle actuators cause simmilar issues like you are having, i would suggest that you physically inspect all engine harnesses for heat damage. specifically the harnesses to each throttle actuator. cut them gently with a razor and look for damage inside. be warned however if these units are bad they can cost thousands each. also if they are defective cutting them open to inspect may compound your problems and not allow the car to be driven. you could start your inspection at the main engine harness if is damaged, you can usually bet the actuators and air mass meter harnesses are as well. all can be a very costly repair.