just a thought my gtr33 was tuned with pfc, ran perfect for about 3 months with knock of around 16-20. then for no reason started knocking to 60. called my tuner ,did the usual things, fresh fuel, checked plugs etc this didnt make it any better the last thing he told me to check was how clean the airflow meters were. they were filthy.i took them off and cleaned them with carb cleaner half a tin on each meter,let them dry and replaced them and knock back to normal give it a try for the price of a tin of cleaner, good look
