C180 power loss.

[tractorboy]

Can someone please help me, I have a automatic 1997 C180 what seems to lose power at the lights, it appears but could be my imagination when engine is fairly hot, but I don't really know.
I cure it by putting it in park, handbrake on, ignition off/on and away we go, does anyone have any ideas. The lambda sensor and spark plugs were changed 2 months back for the MOT, due to high emisions.