My '99 jetta (stick) drops to 5mph and the rpm shoots down at 20 mph or approx 2800 rpm. idles slightly rough (though not much) and at high rev in neutral the gas again cuts out at about 8000 rpm and catches back again once throttle is let up and down again. Can only really drive 15-20 mph before it jerks suddenly from sudden fuel stoppage and then the throttle needs to be let up again and depressed. if it is held down solid during this time i get no engine rev. Codes pulled read p1580 (vehicle speed or idle speed control, throttle actuator b1 malfunction) and p0103 MAF A circuit high input. could this be a throttle valve sticking or throttle body in need of clean or something like a MAF sensor problem needing a reset or being just plain shot? Or another possible malfunction, vacuum tubes?