Mitsubishi Repair: 3rd failed emissions inspection, car mechanic, mitsubishi dealer

Question
I have been driving with an expired emission state sticker on my 1997 Mirage since Feb 07.  I keep getting told: "The sensors are not registering because I changed or removed the battery from the car.  You need to fill up the gas tank atleast half way, turn on the A/C and drive for 20 miles or more without tuning the engone off".  Well, I followed that advice 3 times and all times the cars' sensors don't register/  Untill recently, the car mechanic offered to drive it himself to make sure I was driving it up to par on his commands.  So he was gone for a good hour.  Synopsis:  Some sensors are registering now but not all, or enough to pass inspection...Recommendation (again): Drive it some more, maybe longer next time.  I would hate to take the car to the Mitsubishi Dealer because I know they will gauge my wallet.  Driving nowhere for no reason is also gauging my wallet (I am a student who rides a bike most of the time).  Is the mechanic correct in his methods? Or is there some other nifty tricks in some nifty tricks bag that I could use to pass my inspection?  I am kinda familiar with cars so I will be OK to go under the hood as long as there are no Flux Capacitors involved.  Thanks a bunch in advance  :)

Answer
Gerson: Is this guy for real? The only way I know to test sensors is to code them. In that you find a shop to test your car's computer with their computer. Once this reading is done, the shops computer will kick out any problem with any of the sensors in your car. There is no way a guy driving your car can see if the sensors are work. No way! The sensors are all through your car's engines, the computer uses whatever the sensor tell it to get your car running down the road. Got an AutoZone close by? They will code your car for free and tell you which sensors are out. Then replace them and then you should be able to pass that emission test. How much has this mechanic been taking you for? You can clear the codes on the computer once the new sensors have been replaced by taking off the neg cable from the battery, waiting 5 minutes and putting it back on. But putting in so much fuel, turning on the ac or driving for 20 miles; is a bullshit. Here is another idea if you don't want to believe me. Go out to any parts store and buy yourself a repair manual for your car. And read up on your car, try for a Haynes as they have a good chapter on emission sensors. But still a Chilton manual would work too. You need to get that car coded, to find out what sensors are out, replace them and get that emission state sticker that you need. And you need to get away from that mechanic of your's. As he is taking you for a ride and not a fair or fun one either. Hope this helps and good luck! Linda