126 Fuel Pressure?

[DHA]

560 SEL recently had major overhaul (valve job, etc. etc.) runs smooth, great. City driving, highway driving the car performs superbly, lots of power. But.....until this overhaul, there would be the expected sound of release of pressure when gas cap removed for refueling. Since overhaul, no sound.

Only two symptons of this change. Starting is slightly delayed on ignition. Worse, engine stumbles -no power- if vehicle passes through standing water (~5 inches). Engine recovers after coasting to the side of the road.

Obviously, the driver should avoid standing water. Now that we have that remedy listed, what else is there that could have been unconnected, misconnected, etc. during that major overhaul that would cause this problem?