Anybody have freeze frame data from the code? I'd say do like the above poster said and take some throttle plate cleaner and clean off the throttle body butterfly and the iac and see what happens. And codes will clear themselves after a certain amount of drive cycles without the symptom happening.

 

Sounds like an ISC motor issue which is a separate part, not sure if it is sold separately though.

 

I bet he could find one seperately. I know the mazda's I work on the TB is expensive, mainly because it has drive by wire and has the motor in the throttle body.

 

The local Mitsu dealer solved the p0505 issue for my car, one week so far with no CEL. What they did: they hooked their diagnostics computer to the car and adjusted the idle control motor step ratio (as far as I've seen it); this is shown in field 45 (on their tool) and they adjusted it with a flat screwdriver on the throttlebody to the value 15 at idle with no AC (it is ok if it's between 2 and 25). They said this appears due to fuel quality variations, vibrations etc. I have 10000 miles on my car.

 

I did it myself using an OBD-II scanner I couldn't read the "field 45" but i noticed it caused the idle rpm to change. I just used it to set my idle to around 920rpm. I was at 800rpm.
Was getting the P0505 fault, didn't get it again.

 

I started getting this code after putting on my ported evo 9 turbo, list of mods are in my tag