[Gmecm] GMECM

[lostrecep tion]

I currently have a 1990 Chevy G20 Van. With a V8 350 5.7l engine ECM 1227747

its been running fine until i put dual exhaust on it now its not running 
well at all the idle is very rough at idle and also at slow speeds (most 
notably when its cold out)

Ive been told by my mecanic i can be a number of things but 02 sensors seem 
to always come up as my ecu supports 1 o2 sensor and with dual exhause i 
should technically have 2 ? Right or wrong?

id like to possibly avoid doing a flash of the eeprom as im not totaly 
familiar with it and was hoping that someone may know of a solution to fix 
this problem . preferably not a real expensive one ive invested quite alot 
of money in this truck and really want it running well again

thanks very much for your help -Mike