Jitters on drive gear at stop light

Ok here goes, I HAVE DOCUMENTED THIS MANY TIMES SO I KNOW ITS NOT A FLUKE. Car runs beautifully, only one issue and it is as follows. When I come to a stoplight and if it last longer than 20 seconds the car will shake and feels like its missing, when light turns green I will go and after a few seconds the shaking will stop and it runs smooth again. Now. If I put it in neutral at a stop light this does not happen.
THIS IS NOTED. If the stop light lasts for over a minute the engine will start to shake and it last for approx.
20 seconds then it resumes its smooth idle again, so it sort of goes thru a cycle of some sort.I have been keeping notes on this for a few weeks now and it happens the same always. Stopped at a red light for longer than 20 seconds the idle will get rough and shakey, this lasts for about 20 seconds then goes away. Time after time. Its like clock work. Is there some kind of timing thing in the computer that makes this happen. Granted Ive only had the car for a month and haven't done any tuneup except take out the MAF sensor and spray clean it.A friend suggested I do this
This didn't stop the problem. Any help would be greatly apprieciated. Thanks, Pauli