smallblocks

I recently have taken my truck to my state emissions testing facility I failed the co test.......So I did a thorough check of everything replaced the egr and various vacuum hoses new plugs and wires ....... the truck runs very smoothly sometimes while idling it will flutter but it wont cut off upon a diagnostic the computer tells me that the o2 sensor is rich and there is a map sensor error i have replaced the o2 sensor and replaced the line running from the throttle body to the map sensor....i havent hooked it back up to a computer or been back for emissions testing but i suspect it hasnt changed because it still has the flutter going on.....the injectors seem to be sprayin great ....motor is dead in time i swapped out the map sensor with another that didnt change anything? anyone have any ideas or suggestions....i am stumpped at this point!!!

gto8u

make sure it's getting up to normal temp..as in nobody removed the thermostat. also check engine temp sensor near thermostat...this one feeds the computer and tells it when to engage closed loop
if your in open loop, the o2 sensor is cut out of the circut and idle control is solely by the idle control valve (bottom pass side of throttle body) This could also cause a little flutter at idle since the fuel ratio is running at defalt and no timing advance.
once in closed loop, you get timing advance and O2 sensor-fuel adjustments 5-8 times per second. thus cleaner burn and lower CO reading