I have a 2004 rx8 and it’s been great until about a month ago. The car takes more cranking than it should to cold start, and once it’s running it runs like garbage until the air pump turns off, and then it still doesn’t run great until it warms up. Once the car has warmed up you can’t even tell, and warm starts are a breeze. My first thought was a clogged cat, but I’m kinda new to the whole rotary thing. I also have a lean code (p0171).

 

Unlikely it's your cat as it would cause performance issues at all times. I would guess try cleaning your MAF sensor with MAF cleaner and see if that solves the issue.

 

Any smoke from the exhaust while it's warming up?
Is your coolant going down or bubbling while running?

 

I haven’t had any coolant loss or smoking. I also have a new mass airflow, and I’ve redone almost all my vacuum lines. It just runs like garbage until the air pump shuts off.

 

I replaced my maf a few months ago to try and remedy my lean code, and it made no difference.