2012 E450 4matic, changed the water pump, started the car to check for leaks. No errors, car ran fine. Had one leak up around the thermostat housing. Got that fixed, put everything back together and started it up again. ESP inoperable message on the display and yellow triangle is lit on the dashboard. Car is idling at 1000 rpm, won't go above 1100 rpm with the pedal floored, and seems to be pulsing at idle. My code reader is in another state so I can't read codes till the weekend. The only connector I unplugged was the 4 pin on the throttle body. Is there anything easy to check that might cause this?

 

Sounds like you need to recheck the throttle body connector.

 

yes there is: use your favorite MB scanner to query the ECU.

Next time...: disconnect all chassis power before disconnecting essential modules, actuators or sensors. None of these are really "plug n play" through ignition off but are indeed re-enumerated during a reboot sequence (batts out!).

So reboot and clear faults with a decent MB scan-tool.

### Down scaled MB near HK Island SAR.