my boost was running at 15psi and holding no problem, but it has started to 'bounce' it now goes to 18 and then to about 9 and back and so on, it feels like im driving into the wind for a second!
any ideas it has been serviced very recently?? (its a uk car 99 v)

 

sounds like overboosting to me, then fuel cutting for protection.
you sayit normally runs at 15psi, is it modded or PPP'd.
Mine normally runs at 15psi, my99 UKturbo PPP.

 

Or maybe one of your coils is cracked?

 

it does have ppp!