missing real bad at idle

Hey yall i have a 97 chevy blazer 4x4,4.3 vortec.it has started missing real bad when you start it up and take off.the check engine light is on and i have done put a map sensor on it and still nothing.i put new plugs in it and still nothing.it rides like a cadi. when you get to going but when you slow down it goes back to missing...please help???????is the any way you can check the mass air flow sensor?????

From all the post I have seen on the miss issues, get the codes. Most of them have turned out to be either:
Dirty:
O2 sensors
EGR
Some have been the spyder
 
Look at your exhaust and see the color, check for water. If wet look at the color of the fluid.
Check for coolent in your oil and oil in the coolent.
Check your plugs (mgith be fouled)
 
This is just a small check list to start also might want to use the link above and look over the recalls and TBS for your ride.

I would suggest you have the codes read and let us know what the CEL (check engine light) is telling you. 

The MAF sensor can be cleaned if you are careful enough.  Run a search and you should find numerous posts on the subject.

If you have any other questions, just let us know!

I am an auto tech, and I just had a 2000 Blazer in the shop running the exact same way.  The code came back for a cyl 1 missfire.  After running tests on the engine, I found cyl 1 was low on compression at about 75 psi.  Hope this helps, Korey.

With Korey's info tells me not to go and get a newer used motor LMAO
 
If the rings are failing that soon, sheesh must be a hard driver or goes too long between oil changes.

MNHawk:
Could also be a burned/sticky valve....low compression not always rings....

97blz4x4:
You could have a sticky poppet valve or vacuum leak or carbon buildup in the EGR valve...
Do you have a smell of gasoline when you remove the aircleaner hood on the TB? If so you could have like MNHawk said a leaky pressure regulator/spider...
 
Also are you running an oiled foam filter style filter like K&N, if there is excess oil on the filter it will get trapped on the MAF sensor and cause rough running....

Like Swartlkk said, get the code read first

where is the egr valve located at?????i dont remember the codes,but they read out to beight the maf sensor or mass air flow sensor..