My throttle will intermittently lag. By this I mean that I will twist it and the engine will not respond with an increase in RPMs. This issue most commonly happens when I'm trying to downshift. I pull the clutch in, kick down the shifter, and blip the throttle, but the engine won't rev. However, the engine will usually respond if I blip the throttle a second time. Occasionally this problem will also happen when starting from a dead stop, but not nearly as often as when I'm trying to downshift. Thoughts?