Mojo

I own a stock 99 TL and I recently went to the dealer to get the car checked due to the Check engine light being on. After they checked it out, they told me the problem was carbon deposits on in the air intake which caused some air restriction thus causing the check engine light to go off. The thing that ticks me off is that the light went off two times before this time during the year. I got it checked out previously and they said they didn't find anything worng so all they did was reset the light. The kicker is that my warranty expired early last month and the previous times I brought in the car, it was still covered. Since the warranty was over, it cost me over $225 for them to clean the carbon deposits. I don't know too much about "do-it-yourself" stuff so did I get ripped off? Could I have gotten it done alot cheaper on my own? Anyone else run into this problem with their car?
The service guy told me to use higher octane gas. I already use the recommended level of 91-92. He told me to go up to 94 octane and to go on the highways once in awhile and literally "fly" on it to burn off the carbon.
Sorry for the long post, just wanted to let someone else know about it. Thanks for reading it if you made it this far.