1) make sure that the servo linkages and transmitter EPA are set right with a little gap on the throttle linkage before it actually begins to throttle up after you apply it from the transmitter
2) make sure that the servo throttle linkage moves freely in the plastic hole of the servo arm
3) to me it sounds like a bit too rich on bottom
lean it a bit and lower your idle if it holds high idle
The #3 only if the 1-2 are set right.
If otherwise you need to retune.