Volvo: 95 volvo 850 turbo, haynes book, oxygen sensor

Question
Hello, I have a issue with my check engine light. First off, my vehicle is a 1995 Volvo 850 with a 2.3 turbo engine, that has 124,200 miles on it.  I ran the codes through the Motronic 4.3 system and found three codes. *_Here they are:_*
1. 2-4-1     EGR System flow malfuntion
2.  2-1-2    Heated Oxygen sensor absent or faulty
3. 1-2-1    MAF sensor signal absent or faulty

After I checked the codes myself and looked up their meaning in the Haynes book.  I took my car to auto zone to read my codes with their OBII scanner (just to double check).  Their scanner only found the fault code EGR System flow malfuntion.

My question to you is, what could be the probable causes and solutions for these codes. And what parts most likely I need to replace; EGR Valve, Oxygen sensor etc. ect.  And my volvo is still running smoothly not rough.  Your input is deeply appreciated.

Thank You

Answer
Steven,
Most repairs to the EGR are the valve itself. Although the tube to the exhaust could be clogged, but not as common.
First clear the codes and see what codes return, if they do then.
On the HO2S replace it with a Volvo one and clear the codes.
Replace the MAF sensor and clear the codes.