I have a fuel injected 78 280z with a performance cam. It starts and runs great, and accelerates and cruises smoothly while cold. But after it warms up a bit the throttle is jerky. When making very tiny changes to the gas peddle (just to maintain speed), the throttle jerks on and off. Its great while accelerating or decelerating but just doesn't maintain a steady cruising speed without jerking in and out. This is very obvious at 50 mph or less but doesn't seem as pronounced at highway speeds. Maybe a Throttle Position Sensor? Air Flow Meter? Vacuum Leak?