I've never posted, but I've spent a lot of time reading posts as I've tried to get my 2003 Corolla fixed. So I feel I owe it to the next guy to share my experience. Because this forum and others like it just saved me $1,000 or more.

My trouble started with a CEL that, after I bought a cheap code reader, turned out to be a P0505 code. Encouraged by this forum, I ordered an IAC and put it in (tried cleaning the IAC first to no avail). Success! For a few months. Then it came back. Frustrated and wondering why an IAC would go bad so soon I looked for vacuum leaks and replaced the intake gasket. No luck. I ordered a second replacement IAC (this time a $50 el cheapo off Amazon) but it didn't even clear the code for a second. So I decided it was time to pay the pros.

Took it to a local shop, with whom I have no complaint, and they put in a new Toyota OEM IAC. Which didn't fix it. They told me, after further testing, that I had a bad ECM and that I'd need to go to the dealer because it would require programming/flashing.

I did some more Internet sleuthing and found reason to hope that a 2003 Corolla didn't need individual programming. I found a matching part number used ECM on EBay for $29.99 (shipped!) and decided to roll the dice. Just put it in and lo and behold success! No CEL, idle is what it should be, and I'm on the top of the world!

Never would have had the courage to try without this forum. Thanks all!