I had this happen too. It would go away then come back a few months over the coarse of two years or so... then last month, I was at a stop light and it did it at idle with the brakes on... then it went away. I suspect there is a vacuum leak somewhere, not in the usual place. When I put it on cruise control, no matter what speed, it would fluctuate also...
Anyways, for my case, over time it developed into 1. excessive backfire and misfiring on wot or hard acceleration no matter in motion or from stop. 2. lurching, hesitation sometimes... then finally 3. the car would hesitate and hiccup from full stop when pressing pedal quickly AFTER it was warmed up.
For my situation, so far I found out that those symptoms were indicative of malfunctioning Purge Valve Solenoid... today I changed it with a new one and the car is so far 100% in all situations. No more hestitation, jerking etc... doesn't matter how warm or hot the engine is. I hope this fixes it permanently and won't come back again.
The purge valve solenoid was the very last thing I replaced after: vanos solenoids, oil non-return valves, crankshaft sensor, both camshaft sensors, high and low pressure fuel sensors, hpfp, lpfp stage 3, new fuel filter/regulator, spark plugs, spark plug wires, battery, new tmap 3.5, new map on manifold, new hoses and clamps, new intake manifold from bmp, new throttle body, oil change.... so you see, it was that purge valve solenoid that was the problem the whole damn time. And the part is not even expensive.