hi. i recently got a 2004 rx8. it runs great but once it gets below 15 degrees celcius outside when i start it up and let it idle the rpm meter revs up and down fluctuating about 1000rpm's. it doesnt do it when my foot is on the clutch. eg. itll rev up to 2500rpm then imediatly down to 2000rpm then up to 2500rpm then down......until the engine is warm. Anyone have any ideas whats causing this?

 

Since it is stopping when you put your foot on the clutch, my guess is that your neutral switch is stuck

 

It's completely normal. Mine always did this on the coldest mornings (which do not occur now that I have moved to Windsor).

It stops when you put the clutch in because the computer figures you're thinking of driving off so it gives you back control over the throttle.

 

That's normal......it's sounds awful.anyone else think it's anything different?

 

Yeah, a friend who owns an FC RX-7 mentioned to not be alarmed if the RPM fluctuates up and down at cold start. "It's completely normal for the Rotary Engine" to intermittently fluctuate to "as high as 2500 RPM then settles to 900 or 800 RPM once the engine is warm."

 

Some fluctuation in rpms is considered normal for rotary engines. However, you might want to check your plugs. Unstable idle can be caused due to fouled plugs. Do you know when was the last tune up?

 

It does sound awful. If I had to guess it is because the computer specifies a very rich mixture.

First time it happened to me I ran inside and logged onto rx8club.com and got the very same answer I gave you. Don't listen to all these guys from the sunny South.

 

Ok thanx everyone. Feel free to add anymore comments if u like. I did change the sparkplugs lately though......it runs great when it's warm.:S

 

Your fine don't sweat it. This is normal.

 

yes, like Boffam stated it's normal.
It did it on my rx7 and now my rx8.

 

Hahahaha! When it's getting cold down here we wrap the engine with blankets)))

 

Totally normal. Though if the temp drops below -10F (or so) you can expect 3k for about 10 seconds after startup, then it'll lower to 2.5k, maybe bounce between 2.5 and 1.5k, until it gets its fluids warm enough to idle happily at 1.5k.

The highest i've seen my RPMs go is 3.5k on startup, and that was at -25F. It only lasted for 30 seconds at the most, then dropped between 2.5k and 2k.

 

It bounces up and down like a pendalum. It's not so much a gradual thing. Is this normal.