low idle issue help plz

i have read alot of posts regarding the rx8 idle issues, and still have found nothing that is similiar to mine, right after i bought my rx8 i was sitting at sonic on day and the car at 900RPM (idle) started shaking gearshifter and all. its a bad shake, i took it to the mazda dealership to let the tech see the issue and what do u know, it doesnt shake while he is in the car. lol my luck right? it does it randomly to be honest, it hasnt done it in the past few days, but it does happen at random stopped at a red light or sitting in my yard in the morning while its warming up before i go to work. the tech and i looked at the engine mounts and he said they seemed to be fine. the car has had a tuneup (plugs wires and coils) i have cleaned the MAF, engine oil is in perfect condition. also it does it only around 900rpm, at the time it shakes it kinda goes down to around 800-850 rpm range, i give it a little gas and its fine.... other than this little idle issue my car runs great so far! and i love the eight.