I have a 2004 mazda rx8 gt. It cold starts and warm starts very well. The other day I replaced the battery, and when I started the car, the engine started, and then died. I tried again, and same thing. Iwas able to keep the car running by feathering the gas, but if I let off, it'd just die. I did the brake pedal pump ecu reset, and that fixed things. Now whenever I disconnect the battery it does this. My initial thought was that there may be a cmos battery or something similar in the ecu to remember things, but I'm not sure. Does anyone know why my car could be doing this?

 

Disconnecting the battery does require the 20 brake pedal reset. It shouldn't be messing with idle that much though even without it. You have any engine codes?

 

While not "normal" this can happen. The computer has to relearn the engine and sensors attached to it, and can be unstable for a drive cycle or two. Best thing to do is let it idle until warm, then drive gently for the first drive cycle. It may stall out when returning to idle but it will learn to catch itself.

​​​​​​If it doesn't idle at all I would look deeper into ignition health, vacuum leaks or a poor intake if the intake is aftermarket. Things like that may not cause problems once it learns, but can make it difficult while it's learning