Is it normal when it Idle's at around 4200-4000 RPMs for a couple of seconds? The RPMs gradually drops and idle's fine. This happens when it's around 10 F degrees or lower. However, I have to hold in the clutch for around 30 secs or the car starts to idle rough/shake like crazy, as if it was going to stall.

 

Not normal to idle that high.
I suggest cleaning your throttle body and MAF. Also replace the MAF O-ring and check for vacuum leaks.

Any mods?

Edit... Ah... 10F... that's pretty cold. (I was thinking in metric eh!)
I guess 4K RPM is pretty normal.

Maybe your neutral switch is sticking in the cold? That would cause a rough idle.

Also you may want to change your transmission fluid to synthetic to prevent it from getting super thick at cold temps.

 

The exact same thing happened to me today. I went to start my rex and it went straight to 4k for about 10seconds. It didn't get rough with the clutch released though. I guess its normal, except for the shaking and stumbling. It might be the coils... I'm upgrading mine soon.

 

high rpm when its really cold is common... I park my car outside and fire it up almost every morning and when it starts getting under 15-20 degrees F i get the same thing.

 

Here! for all of you read this https://www.rx8club.com/rx-8-discussion-3/starting-car-24-c-sharing-experiece-208136/
Thats when i was starting my car at -11F or -24C The high and bouncing rpm are normal but if you keep the clutch in the iddles get a bit better

 

Whenever it was down to -12 F one winter, I'd start her up and she'd shoot the RPMs to 4000-4500. I'd tap the throttle and down it went to the usual 2000. Scared the **** out of me at first!

 

Same here, 9F. I had shaking until I pressed on the gas peddle to make it stay at 2000 RPM for 20 sec. After that it idled at the norm.

 

Nice thread res batman! (You searched yay!)