Strange tuning response on my engine?

[Mr Jody]

Dan – I recently experienced a response similar to yours. Although on quite a different engine (six cylinder – one barrel – it’s OK to laugh), the principal is the same. While investigating some surging and rough running when not at idle, to take the PCV valve out of the picture, which has a line routed directly to the intake manifold, I pulled it out of its grommet on the valve cover and taped over it for a test run. Upon return, with it still idling, I pulled off the piece of tape, which allowed a flowpath through the PCV valve directly into the manifold, and the idle immediately increased. As Jim and Gary stated, this additional air below the throttle plates provided more combustion air. Keep in mind that at idle, the throttle plates are nearly closed and the engine is starving for air, so any additional air, unless already running extremely lean, will benefit the combustion process.