When im warming my impreza up after about a minute it starts hesitating a bit like its misfiring but goes if I rev it then it goes back to running normal again. I am using NGK PFR7B spark plugs at the moment and was wondering if I went back to NGK PFR6B this might cure it?

 

hi m8 mine did the same thing.. and it doesnt wana pick up speed nicely? seems like its really struggling. it judders on idle quite a bit as well? just had the exhaust replaced and cat removed (as once the cat-on-fire light came on).. but the problem is still there?

 

mines only doing it for a short period between when the engines cold and hot,