I have a bit of a problem. When I push the gas halfway down. My car hesistates a bit like I am tapping the pedal. I don't know what it is. It started about two days ago. Today I ran a fuel system cleaner and changed my oil (mobil 1 of course). It is still doing it. Not as bad. I notice it more when my car is cool or has been sitting for a while. It doesn't do it at full throttle. Help me out fam!!!