Cold start problem?
 

Im not sure if this is a problem or not but I've been noticing when its at or below freezing my car takes an extra second to start and when it does start the rpm's move up like normal to around 2k but at the same time im also noticing my engine is sputtering and when it tries to rev past 2k and you can feel the motor shaking like the timing is really off. After the car is warmed out, it goes away and it only seems to do it when its around or below freezing. My RX8 is an 05 M/T with 55,000 miles.

Please give us the history on your car. The service it's had parts replaced. Did you do all four coils , wires and plugs? Type of driving it gets(long commutes, short trip), fuel used(reg or prem), ever flooded. Just any thing that you can add. Have you cleaned your MAF sensor? Done any decarbon cleaning?

Well in 2009 it had new plugs, a new air fliter installed, been following the recommendations in the book. My wife has been driving it mostly on the freeways to work and back. We make sure to use premium fuel and check the oil every other fuel up. Its been in the shop a few times for warranty work, had the motor mounts replaced, clutch pedal replaced, they replaced some body items etc etc. We bought the car with 30k and its always had a rough idle, was worse before the dealer changed out the motor mounts but still get the rough idle and its worse with the A/C on.

I hope you put in OEM plugs and it would be a good idea to check wire connection. I would recommend replacing coils, wires (half-hour) and add a can of Seafoam to just a quarter of a tank of gas and ring it out. Then if that seems to help a little then run another can with another quarter tank. Though this is not as good as a dealer ZOOM-ZOOM cleaning it can maybe give you some direction.

Well the dealer did all the work, I even took it back after I noticed the engine was still vibrating at idle, and the dealer looked and made sure the plugs were ok. I did Seafoam it a few months back, seemed to help alittle with the idle. I guess im going to have to change out the coils myself, dealer said they are fine, and they would throw a CEL if when they went bad. Im going to get my anitfreeze changed today, had the car now almost two years and I dont think its ever been changed.

The coils and wires might be fine but they are a well known maintenance item. I believe the 2005 RX-8 was the first year they added "FL22"(look on coolant cap) which was good for 5 years or 60K miles. Have you cleaned the "MAF" sensor and reset your "ECU"? This only takes a few mins. look in the DIY section this might be the real fix.

I kinda had that problem. I have an 04 M/T but whenever I started it up it would rev itself up to 2k and then drop below 1k and constantly do that for the first two or three minutes. And it felt like the car constantly wanted to die.
Changed spark plugs, ignition coils, wires..
Problems gone. ... well 50 miles after that my clutch went out on me in the middle of the highway..
but I mean.. now the problems solved :)