Okay this one got me going as well... struggling to figure out whats causing it...
First issue what is the stock boost a T28 from S14 will provide... Mine only gives 0.4bar, bit weird thought it should be like 0.7
Second. Above 0.6 the car surges, but extremely bad (it feels like your slamming brakes) then it backfires once or twice then goes...
I got my theory on the second issue, but I first want to hear some other peoples opinion.