Been having trouble with a 2011 Savana with an engine surge at light throttle pressure from 1,200-1,600rpm. You can push through it by adding throttle. The dealer said it needed the the fuel system replaced. That was done. Only to have the problem still there. We replaced the crank sensor suspecting a breakdown in the signal, no luck there either. Short of replacing the ECM, I'm running out of ideas. Anyone have any experience with fixing this problem?