The Fuel Pump Relay is in the MAS on my 92 300E with same issues. Is there a way to check the MAS, or are there codes that may be set and how can one get to read codes without taking to mechanic.

Have replaced rotor, cap , OVP Relay, plugs and checked hosed for leakage. Had to replace right side hose on Idle Control Valve. Still stumbles, just would like to know if MAS can fix this issue.