Just a quick question in regards to my VX L67 AUTO ...mods are CAI and 10psi pulley When I go down hills or rolling with foot not on accelerator I get rev pulsating of about 200-500rpm .. I don't think its a blow headgasket as the oil is clean the radiato

How old are your O2 sensors? The reason I ask is that it's very likely that the car is going into close loop (basically relying on the O2 sensors for fuel metering) under these conditions. As soon as you touch the throttle, the car goes back into open loop and relies on the MAF for fuel metering. Now if the O2 sensors are in accurate working order, then you shouldn't experiencing any issues under closed loop conditions. However if they're not functioning properly then it may cause the hunting you're experiencing as the measured air fuel ratio from the O2 sensors is not accurate. I can't guarantee that tending to your O2 sensors will solve your problem, but it would be a good start IMHO.