Mitsubishi Repair: 99 Mitsubishi Galant Es V6, mitsubishi galant, oxygen sensor

Question
I've owned my 1999 Mitsubishi Galant Es V6 for about 4 yrs and within the last month it started to mess up.  First, I NEED AN INSPECTION so i took my car to a local mechanic and he told me it wouldn't pass because i needed an oxygen sensor.  I got the oxygen sensor put in, then he told me it wasn't going to pass because my check engine light was on.I had an exhaust leak.He put flex pipe on the exhaust and while in the shop my starter went so he put in a new starter.  When i went to pick up my car he didnt do the inspection because he said after reseting the service engine soon light you need to have at least 40 miles on the car before it could get reinspected- so he told me to drive in for a day,and bring it back the next day for the inspection. Well 2 minutes into     
driving it home my service engine soon light popped on again!
All this money and still no inspection--now hes saying its the thermostat-he said it needs to be hotter, but on my temp
gauge is right in the middle-not hot-not cold- i just dont
want to have him put in the thermostat-pay more $$$ and then  
him tell me theres another problem--HELP!!!!!!!!!!!!!!!

Answer
Gianna,
Your thermostat is fine.  Your problem is most likely an emissions component.  Though it's obvious your mechanic either does not know what he's doing, or he's trying to rip you off with unnecessary parts and labor.  I'd highly recommend taking your car to a different mechanic to get it diagnosed properly and fixed.  If you do not know of any other mechanics that would know or you don't have confidence in, take your car to the dealership.
Good luck!