Mitsubishi Repair: Emission test failure repairs, valve cover gasket, egr valve

Question
I have Mits galant 1991 model. It failed emission testing recently and got it repaired. Mechanic changed distributor cap, spark plugs, valve cover gasket and emission test failed still with worse numbers. I took it back to mechanic, he said i need to change the sensor as it controls the fuel flow into the engine. I don't trust this guy as he already took $500 for first repairs without a result. Please advice me on what could be the problem in my car ? Any ideas for cheap work-arounds (well, I got  a waiver, but my car is eating lot of fuel)


Answer
Siva,
A car that uses excess fuel usually indicates a bad oxygen sensor.  That may be the sensor your mechanic is referring to.  Another possible problem could be a clogged EGR valve (Exhaust Gas Recirculator).  That value is reponsible for re-burning any exhaust that may still have fuel in it.  It's purely meant for emissons reasons.  

If you want to save more money, find a different mechanic.  The items he originally replaced have little to do with passing emissions tests.  Plus, those parts and labor should not have cost $500.

Just take your car to a new mechanic that a close friend or family member might recommend.  Have them check the oxygen sensor and the EGR valve.  
Good luck!