2002 2wd Blazer 4.3 V-6 throws po 300 random misfire, 172 rich fuel mixture,175 rich fuel mixture . The engine runs smoothly, no detectable miss until it warms up to normal operating temperature check engine light returns and it registers the codes listed above and begins missing. Have installed new plugs & wires, different fuel pressure regulator, fuel pump registers 72 lbs when checked at 3000 rpms. I have also cleaned the MAF twice since I encountered this issue. Anyone have any idea's? Checked for vacuum leaks and cannot detect any. Appreciate your thoughts and idea's. thanks.

 

After it warms up and you have your problem, Try unplugging the MAF sensor.
This is obvious but check the air filter as well. Never know when you have mouse nest....been there.

 

first of all, for search's sake, it's "Pee ZERO" 300, 172 & 175. Just to help out a bit.

look here for p0172
here be p0175
and finally the whole list of goodness

a lot of 0175 and 0172 over lap so cleaning/checking certain things is helpful for both (i.e. EGR, MAF, etc).
I'd lean toward your o2's giving up the good fight, BUT that's just a hunch... there is still of ton of crap to check, don't just buy parts and throw 'em at it. GL

 

Appreciate the input. Yesterday I cleared the codes and drove it about 6 miles, didn't reach normal operating temperature and didn't get the miss or codes triggered. Today we are in a blizzard here near Kansas City so I won't be getting out didn't mention I cleaned the MAF sensor twice already and I will add that to my original post. I suspect the problem will still exist when drive it further and it reaches normal operating temp. Thanks for your suggestions.