You have to be sure your idle is set, first. Many times when a car comes in to the pits with a "hot" idle - the idle/low end needle balance is off. The tuner will head for the needle on the bottom - the problem is the idle setting. Be sure to confirm your system has no leaks (pressure system or exhaust system) - none!

I like to tune with a very low idle - (with the motor close to temp) I rap the throttle... the motor should fall right to a perfect idle no climb no fall off. With a low idle, if the idle increases (right after the rap) it is lean on the bottom - fatten slightly. If the idle decreases or stalls it is too fat. That requires some practice - but, it is the key to tuning. I can bench tune the bottom and focus on the mid and top end on the track. On rare occasions we may work the bottom tune to gain some punch out of the corners. Best you don't try this trick.

I can tune the car to idle smoothly for 5 minutes or 10 seconds. The tighter the compititon the shorter the idle window. Every track has a slightly different tune requirement.