I had my injectors replaced 7 months ago. Since I've had them replaced my idle has been erratic when the car is warm. It goes from about 900 rpm to 700 rpm and the car starts to knock at 700 idle. The idle raises back to 900 then falls again to 700. I was told when you have the injectors replaced the car's timing gets messed up? Any suggestions? I've checked for air leaks and fixed a bunch.