I had quite a scare about a week ago.
Returning from a daylong hike with temperatures in the 40's, I started up the Sprinter, let it warm up for a minute or so.
Checking in both directions for traffic (none seen), I put it into D (drive) and being pointed downhill, it rolled away easily. Cranking the wheel to turn uphill, I was now straddling both lanes on a blind corner at night. The accelerator pedal had NO EFFECT, just as described.
I immediately floored the accelerator pedal and held it there. The Sprinter would not move. The engine did not die, but it would not go anywhere either. I do not recall if the RPMs dropped in this case, being more shocked and afraid of being hit by an oncoming vehicle, but at the least there was no increase in RPMs.
Slowly, reluctantly, about 30 seconds later, the Sprinter started going and I drove away. Once warmed up, it behaved normally as is always the case.
Lately, even on relatively warm nights (not much below freezing), I cannot get the Sprinter to move (R or D) until warmed up several minutes. With colder temperatures, it 8 to 10 minutes to go anywhere, dropping to 500 rpm and lugging badly and going nowhere. Put into N or P, the engine RPMS are as high as 1400 when cold, and the engine revs freely when pressing the accelerator pedal.
The following diagnostic code is found:
ECM-EngineControl ($7E0) P0506 PowerTrain Confirmed Idle Air Control System RPM Lower Than Expected