What Causes a BOV Pressure Leak?

A pressure leak in your air intake system caused by a leaking blow off valve (BOV) can be caused by a couple of different problems. Most blow off valves operate on the principle of difference in pressure. When there is low vacuum pressure in the intake manifold because the throttle is open, the blow off valve will be closed. However, the boost pressure can push the valve open a small amount, allowing this much of boost pressure to escape/leak. Also, if the engine is at idle, the increased vacuum pressure in the intake manifold can cause the blow off valve to open and cause a leak.