I have a 04 rx8 manual with 60K on it. I purchased it 2 months ago and since I did not know when the spark plugs and coils were changed I decided to change them. I am new so I got help of one of my coworkers who is very good mechanically. I changed all spark plugs, wires and all coils. I have a stock air box and to do that I removed air box and the accordion tube. I put everything back together and the car started fine. I let her warm up and started driving home. Everything was smooth and actually I had more power until I tried to stop at stop light. As soon as I go to neutral and brake, the RPM goes way low (below 500) and sometimes the car stalls. I can start the car again immediately and the RPM is fine until I drive and try to stop or I apply gas and let go of it.

After that I checked all plug wires to make sure they are connected correctly and checked all vacuum lines and they were good.

Did anyone else have this problem before? I need help!

BTW I disconnected the battery and reconnected it, is this related to removing the battery?

 

Disconnecting the battery resets the fuel trims... so you'll notice some idling problems for a couple drive cycles.
I would double-check the ignition components and make sure they are correct.
Which spark plugs did you install?
Did you verify the leading and trailing plugs are in the correct port (the engine casting has an "L" and "T" on it)?
Verify the coil order to the plugs:


Again... idle "weirdness" is common while the trims are relearned, but if the car stalls, that can indicate other hidden problems.
Usually ignition is one of them, but you just replaced those.
I had the same thing when I used RX7 plugs, everytime the battery was disconnected I would stall at idle until the trims were "retaught".
After I changed back to OEM plugs, I never had that problem with disconnecting the battery.

 

Thanks Jon,
Well this was the first time I was doing such a thing and I was triple checking everything before tightening so I am sure I put the right plug in right position. It took me about 4:30 hours so you can guess how careful I was. I used NGK plugs and wires from THMotorsport and OEM coils from Mazmart. I also marked coils electrical connection and checked the wiring again after I had the problem.

I was thinking about fuel trims too since it idles fine after start but if I apply gas and let it go then the RPM drops low and if it don't stalls it goes back to 820. I also have a scanner that can monitors live data but I do not know what I should check. Again I appreciate any input from you guys since I am just learning about this car.