2003 ML500. Starts out driving fine, then after a few minutes loses power and does not accelerate at all. You can push the pedal to the floor and lucky to go 10mph. If I kill it and restart it is fine for a few minutes, then happens again. No other lights other than the check engine, and no other codes other than p0123. I've searched and found a similar problem with the S class, and it was the actual pedal module. Anyone have the same issue?

 

I checked the Star Manual and any P012X is incorrect voltage of throttle position sensor or throttle body actuator. I would check and clean the electrical plug (without removing it) also manually cycle throttle valve for full return and correct mechanical operation. If this dosn't help, you can remove it, open up plastic cover on the side and you will find 3 open style carbon potentiometers. One of the wipers could be dirty, giving out faulty readout of the throttle position. Easy to bench test with ohmeter.