I bought a 2004 Mazda RX8 with an automatic transmission on December 20. At first all I needed for it to start up was a battery. So I bought a Duralast Gold battery and put it in. After some crank, the car still wouldn’t start, so we put some jumper cables on it. The car finally started and I was able to drive it. But then the car died.
After a few attempts to get it started again, it starts up and I realize the car can’t go below 1000 rpms. If I take my foot off the gas it’ll go below and turn off. So at every stop and turn I make, I have to have at least 1000 otherwise the car will turn off. Can anyone help me and determine what it may be?


Here she is after a needed bath

 

First thing to do is a proper compression test with a rotary compression tester. Ensure you are not throwing parts at a tired engine. This is where I would start.

 

Able to scan for codes? Compression test also a very good idea.

 

I replaced the starter and spark plugs. The car starts up within 3 seconds of cranking now. She won’t start hot though and the CEL is still on. I was able to get the codes. It came up with two.
Unfortunately, my mother in law threw the paper I had them written on away, but I do remember the narrative.
1) Secondary Air Injection
2) Evaporative Emission Control System Leak (Large)

I did some research, and for #1, I keep coming up with the Air Pump, and for #2, I come up with the gas cap. Can anyone confirm or deny that this MAY be the cause for my car not starting while the engine is hot? I know it can be low compression, but a bad air pump can cause this too, right?
At this point, I’m praying I don’t have to replace the engine.

 

The air pump does not affect the engine's ability to start. Its merely an emissions device used in cold starts. A large evap leak can be a gas cap. But it can also be a vent valve or purge valve stuck wide open, a hole or crack in the canister, a rusty filler neck etc. There could be a number of causes. It should be properly diagnosed and if you toss a gas cap at it and it doesn't fix the issue, it's time to use a smoke machine to see if there are any large leaks that are visable. If not, then you likely have a vent valve or purge valve hanging open or another issue with the evap system.

You really need to do a proper compression test with a rotary compression tester before throwing more parts at the car.

 

3 seconds for a cold start is still kind of long. Not horrible but could be an indicator of another problem.

Starting cold but not hot is a common sign of low compression. Get a compression test done before you throw any money at the problem. If that comes back okay, check your fuel pressure.