My 06 Mazda3 iTouring 2.0L engine auto tranny with 53K miles - the engine idle is rough when stops at stop sign/red light, at about 500 RPM or less. According to a thread on the Mazda3club.com

http://www.mazda3club.com/showthread.php?t=55342

Someone suggested the problem could be at the fuse box corrosion where the horn and brake fuse has impact on this rough idle. Anybody has any advice on this? And is there a way to adjust / increase the idle speed without reprogram / touch the ECU?

 

I had the same problem after intake install. Did you recently disconnect battery?
Anytime you disconnect battery, ecu will reset. Your car will try to run assuming car has 0 miles, brand new. Which it's not. So here's the fix.
DISCONNECT BATTERY, drain power fully! You want to Reset ecu.
I would first just spray the mass airflow sensor with cleaner. Make sure it's the right stuff.
​​​​​​​Then turn the car on once everything clean, installed and ecu has been cleared. Let it just idle for 20-30 mins, don't touch it. Then turn on ac full blast for 15, don't touch it. This should let the ecu remap itself. Once you go to drive it, drive like a granny for half hour. Don't floor it. Gotta train the ecu. Should be all set.