Could be an intake manifold leak, loose vacuum hose, or if you've done some major work to your engine that involves plugging/un-plugging electrical parts, you could have the harnesses of the AICV and IAT sensors crossed. Same plug. Usually accompanied by a check engine light with code 14 if that's the case, though.

If too much air gets past the throttle body or if there's a leak and your engine revs too high, then the ECU will kill ignition to drop it back to where it's supposed to be. The ECU won't do this until the car warms up and goes into closed loop. If one of the sensor doesn't report properly, the ECU stays in open loop attempting to correct the problem.

Low coolant can cause it also. Or a bad coolant temp sensor. Usually that will trigger a check engine light also.

No check engine lights, eh? If not, then do a search for "intake vacuum leak".