Volvo Repair: Sensors, mass air meter, mass air flow

Question
'92 740 Turbo Wagon w/226,000 miles on it (you recently answered question re: fuel leak which I was able to locate and fix after your response-thanks!!!)  In preparation for smog, had diagnostic done (& oil/filter changed & brake fluid checked and filled so that no problems there with idiot lights) and four codes were detected since my check engine light has been on & 4 diagnostic trouble codes were detected: 121, 113, 322 and 413 and they recommended replacing the mass air flow and EGR temp sensor ($650.00).  Are these the same as the idle air (control valve) temp sensor and the 02 sensor?  And Volvo called them MSF sensor and temperature sensor, so I want to be sure which two sensors we're talking about because I read that it's possible for ME to check them and/or replace them.  Labor is only $50.00 ($200 or more @ Volvo) if replaced, new.  So, can these be pulled at a Volvo wrecking yard and used to replace mine and are they really that simple to replace?  AND THE QUESTION IN MY MIND IS, DO THESE SENSORS MERELY DETECT OR DO THEY ALSO AFFECT THE PERFORMANCE OF MY CAR ('cause I may then get the engine light out and pass SMOG, but still have some other air/fuel, timing belt or transmission problem that could also cause the symptoms I'm experiencing that Volvo said could be resolved when the MSF is replaced)?  This is allot of money to spend for SMOG when 2 yrs. ago, BAR's CAP program sent me to a place who detected a transmission error code and reset it and I passed = to me this had nothing to do w/SMOG but that check engine light had to be out to pass and now I'm starting with the same problem - that check engine light!  Thanks for your help in the past and the future.  

Answer
Wow Ruth,
      My eyes are burning..all your info has me confused..I'll try to answer.
         The AMM (mass air meter) either works or it dosen't..if the car runs better without it connected to its electrical connection..means that it is failed..often these AMM's are available on the internet for a lot less money..like $200...rebuilt and considered after market product..they work ok..often they will want your old one.
  They are referred by the last 3 numbers listed on the part..005..or 007.or whatever...different years have different numbers...only the exact number will work.
Junk yard parts can be good...but install it there (super easy job)if you leave the property and find out it also is failed..too late..they DO NOT TAKE RETURNED ELECTRICAL COMPONANTS)
        The E G R relates to recirculating exhaust gass'
        I'm not sure how it relates to the emissions..the Idle control valve is a part that regulates to the low speed and idle performance..
         O2 sensor plays a major role in emissions..if it's the original part..I'd replace it..it is connected to the exhaust and can be tough to remove it...tight spaces to work in..if you have the RIGHT wrench it can be done by you..
        Next time you get tested for emissions be certain that car has had a high speed run on the highway(over 60)
add 4 bottles of dry gas before you start your highway ride..into less than 1/4 of a tank of gas..this'll help
          There's lots more that could be said..but this'll get you into solving your problems..
      Happy motoring,
                     Bilbo