Don't mess with the idle or the mechanical screws, the DI throttle bodies are synced together and are almost impossible to get them right even if you do know what you are doing and have the equipment. Poor idle can be caused by several things, start with the basics, check compression. Did it run fine after the injector was replaced with all the current settings? Could be as simple as resetting your TPS, but you'll need BUDS. PPG in south FL is the best in the business with DIs.