2005 Legacy Outback Rough Idle & Stall

Make: Subaru
Model: Outback
Year: 2005
Mileage (at onset): 60,350 (approx)
Current Mileage: 61,050

I took my vehicle in to have an error code checked (turned out to be the evap code. Aka loose gas cap), had the code cleared, filled up at the Exxon (87 oct) and returned home. Two hours later my wife started the car in the garage and said it sounded funny and the steering wheel was jerking. As she pulled out of the garage the car stalled.

She restarted the car and it stalled again. I switched vehicles and took the car back to my mechanic. They rechecked the OBD to see if any (new) codes existed. Nothing was present, but they said their equipment wasn't updated for the 05 Subarus and for me to take it to the local dealer.

The dealer evaluated the car and said the OBD had no codes, but the air filter was dirty and replaced it. Said it was running fine. I paid the $97 for the air filter ($75 of that was for "diagnostics"), but when I pulled the car from the parking spot (not lot, spot) it stalled.

Went back in and the mechanic said it must be the O2 sensors and would run me another $175 plus labor. I decided to get a second opinion.

Went back to my mechanic and had them do the 60k maintenance (we were scheduled to to it the next week anyway). Replace plugs, fluids, and God knows what else. All the stuff the 60k was supposed to have done. Also cleaned the throttle box and added a can of 44k to the gas.

Problem still existed. Thinking it was bad gas (remember, I filled up RIGHT before problem started), I added some dry gas (I know 44k should take care of this, but a little more couldn't hurt if there was a lot of water).

I am now on 2nd FULL tank of gas since additives. The current tank is 93 oct to see if problem improves.

Throughout all of this the car has run perfectly at speed. The fuel economy is still normal (nearly 29 mpg on highway).

On the way home finally got another Check Engine Light while idling at the gas station. So I purchased a Innova 3100a at the smiley department store (sorry, no free advertising from me!) And got the P0506 - Idle Air Control System RPM lower than expected.

I am going to return to my mechanic to see if he can test the MAF sensor to see if this is corrupt. I am seriously put off by the dealership because of the $100 air filter that didn't fix the problem. So I won't return there unless I absolutely have to.

Is there anything else short of replacing sensors until the problem is fixed. I have a bad feeling the last thing replaced will fix the problem (and that will end up being the computer)

Thanks in Advance.