I love my rx8 and have no problems except for this.

I have an 04 AT 4 speed (I know I know) /w 20k some miles on it.

I bought it used so I'm not sure if this problem came from the start.

Whenever I run the car right around the 30 mph range, the rpms will suddenly drop or kick up as if its shifting gears but its not. If I hover around that speed (either in 3rd or 4th) and hit the gas it'll rock forwards and back until I speed up or let it slow down again (like its shifting gears but a little more rocky). From what I can tell, the direction of rocking is along the direction of travel, ie forward meaning down the road and back meaning reverse.

The problem is really bad if I run it cold (before the temp needle gets to middle). When its warmed up, the problem isn't nearly as bad. For this reason, I've been letting it warm up before driving it in the mornings or at least run it really easy until then.

Any ideas what the problem could be? Is this normal?

There are absolutely no traces of this problem at normal highway speeds (cruising 50, 60, 70 mph) and when I run the **** out of it.

EDIT: oh yea. It'll idle high (like at 2.5) when I start it up and its cold, and will SLOWLY settle down to the 800 rpms range as i let it warm up in park.

 

RPMs are increased when engine is cold to help warm it up, so that's normal.

About your problem.. sounds a lot like when I try to start in 2nd gear and let the clutch go too soon, it sort of rocks back and forth until the RPMs go past 2k.

 

What gear are you in when it does the 30mph rock? If you are in the "Auto" mode, it's the transmission shifting into and out of overdrive.

 

trans slip....... maybe? Does it feel like your in neutral and the trans is trying to shift? Or is it just not shifting at all?

 

it does it in 3rd and 4th. Its rougher in 3rd though.

 

Auto mode or manual mode?

 

auto mode. I may have felt it once in manual mode but I can't remember

 

Try driving in the Manual mode, don't let the RPM's drop below 2500.

 

It def happens only when the needle dips low, like below 2000. So i'll give that a shot.

 

30mph in 2nd gear = 2700 rpm.