hey guys, got a problem here and i was hoping maybe someone on here could help me (Before i see a mechanic if i need one). a few days ago i drove to virgina to pick up my brother from my dads place, on the way there i had to fuel up 4 times (i live in SC). my car is a 02 Honda Accord with a CAI, Headers and a catback exhaust, so i thought it was strange that it consumed this much gas. When i got back home i told a friend about it and he told me that i might have to reset my ECU, that maybe my car was trying to run based on the "old" airflow rather than the new. so i disconnected the negative terminal on my battery for 30mins and let it sit, after the time was up i put it back on and started the car.i instantly noticed the my stereo no longer works, it doesn't power on or do anything, i tried resetting it, checked the fuse on the back of the unit, checked all relating fuses on the car, and even tried connecting the positive and negative wires of the stereo to the battery, but none of it worked, it still does not power on. is the radio broken, or am i just doing something wrong?

also the idle is now very low (usually its up around 1000rpm's) but it now idles closer to 500rpms. when i drive for a little and come to a complete stop, it goes down to almost 0, like it's about to die, but then goes back to 1000. is this normal, or would you advise to take it to a mechanic? i can provide a video of the problems and provide additional information if it helps.