It'll probably be the coil packs. I've had one go on both my 20VT's. Borrow/buy one and take it for a drive, placing it in each of the 5 pots. Only takes 4 min to unscrew the coil pack cover and change each coil pack. They deteriorate over time and cause misfires, loss of power, spluttering, and rough idle. It's only £15 for a s/h coil pack. Or it could be old or new but faulty spark plugs, I've had that too.
Regarding the possible spiking, I forgot the first, easiest fix - remove your existing EBV and give it a good spraying with WD40. sometimes they get gunked up and are slow to react to boost.