VAN STARTS BUT NO POWER,WILL NOT GO OVER 20MPH.

Hello, which engine is your Sprinter equipped with? Sounds like a fuel delivery concern, an air intake restriction concern, or an exhaust restriction. Could be an engine timing issue also. Not much to guess at here without knowing a lot of other information - most of which must be found by checking the vehicle first hand. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops