I have just recently changed the plugs in my car to Ngk iridiums, I now seem to have a flat spot under load in 2nd and 3rd gear round about 4-5000 rpm. Could this be the plugs, I have checked the coil packs and one had a crack in so I replaced that but still the same.
It's just frustrating me now what it is, can anyone help?
Car is 1996 wrx import

 

Boost control solenoid? Give it a clean sometimes works and sometimes doesnt as never worked with my one. We werw getting a flat spot at 4200 rpm and it was a sticky solenoid

 

Your an absolute diamond mate, it wasn't that but the hose from the solenoid to the turbo was split!! Drives absolutely spot on now so pleased. Many thanks