2007 hawkeye bucking as boost kicks in

[Piggysniffer]

Afternoon all, I have a 2007 wrx wagon that pretty much drives good, randomly I will get a bucking as boost starts to come in, it's pretty savage sometimes, enough to throw you about in the seat, it is random and only happens in 1st and second mostly and the boost gauge will jump up to 10-12 psi and back to zero when doing it, the afr will also jump around but I presume that is to be expected, at any other time the afr is good, a steady 14.7 - 14.8 while of boost, going to 10.4- 10.5 at wot with a good taper from the start of boost, I honestly think it could be a dbw throttle pedal issue as when I bought the car the pedal stop was missing from the floor, unbeknown to me, I found it in the glove compartment when I got the car but had no idea what it was until a few weeks later, have no idea how long it had been off or why, but I had mashed the pedal down a fair few times myself without it on , I then read that not having that stop could damage the pedal sensor/casing and to be honest it looks a bit bowed in places, just wondering if anyone else has heard or had this sort of problem

Thanks in advance for any help guys/gals, I'm going to post onother thread about logging the car also