have you cleaned the fuel filter??
Also i once had a surge problem when cornering in my 16V sprinter and i had a surge tank.
Basically there was a plastic fuel filter in the low pressure hose coming from the lift pump to the surge tank. Now the filter itself was fine but what had happened was someone (probably me) had tighten the shit out of the hose clamp and crushed the bit where the hose goes onto the filter cutting the flow diameter down to nothing. So the surge tank was always very empty. I was lucky i didn't burn out the high pressure pump starving it all the time!! Oh and the fuel getting shoved through the small gap made this wierd howling squeak all the time so replacing the filter fixed that too