Tech Tip No. 15
Originally published in the quattro quarterly
Engine Stalling - Leaking Bypass Valve
This valve is found on all 20-valve turbo engines beginning in 1991.
The valve reduces the peak pressure spike when the throttle plate
slams closed during each gear shift, saving the intercooler from rupturing, and keeps the turbo spinning during the shift. In some cases it even reduces turbo lag.
However when the valve leaks or the hose from the intake
manifold which operates the valve with vacuum and pressure is pinched, or cracked maximum boost pressure is reduced.
In addition when the valve leaks the engine will stall after pushing the car hard when you come up to a traffic stop.
Replacing this valve will return maximum power and eliminate the