This might sound really retarded but my rpm gauge was way off for some reason and the car didn't have any big problems, but i didn't find that also my mph gauge needle broke when fixing the gauge.
My milage of my car does not go anywhere, so in that means no matter how much i drive it the milage don't change and with the needle broken i can't tell how fast I'm actually going but i can only judge the speed.
The engine was fine and like i said before my mechanic told me i would need to get the carbon cleaned out and get the injectors cleaned up as well, so the only thing i found wrong was an exhaust leak at last.
My engine idles fine at 800 rpm and once warm enough to drive it drives real good even better than when i bought it, but all i have to deal with is the exhaust leak, the injectors and cleaning the carbon out.