if you are getting code 34 then that is all the conzult or datascan will tell you, what you are really trying to find out is wether you are getting dett or not and that is a lot harder to diagnose, what most people do is fit a resistor in the wiring loom to the dett sensor to fool the ecu into thinking there isnt a problem, only drawback to this is if it was dett causing the issue then you just removed the cars way of protecting the engine, do a search on detonation and theres loads of info, the trim under the windows wont look good painted and youre best off getting either new trim or second hand good condition stuff from SWZ , i have sprayed the front window side trim satin black and it looks ok and im also going to do the targa top trims like this, as for 18's on a stock set , cant help ya there as mine is lowered and uprated