I bet it's not injectors...on sparks plugs there's this thing called heat rise and disappation...the rate spark plugs recieve heat and then cast it off...very important stuff....very important. If you don't have the proper sparks installed things like you say can happen. I had a BMW 633 that required silver tip spark plugs due to heat disappation matters...believe me, the damn would not run right until I put the Silbers in, as the box said.....$6 each...don't screw around with the spark plugs.... they seem simple and stupid, but they are as important as your tires....