91 sonoma, no closed loop.

hi,

my 2.8 sonoma wont go into closed loop operation. i replaced the..o2 senser and the cts.
also the thermostat, so it would get to operating temp.
it just wont go in closed loop, also runs lousy...help.

also when i scan it with a snap-on modis the engine temp. is normal...o2 working ok..but shows not going into closed loop? also the idle is a little higher, about 1,000 rpms. no vacuum leaks preasant etc.

when driving cold the truck runs great, but when warm it acts-up a little.

i,m leaning toward the ecm?
any ideas would be a great help...thank you.

Just a guess, have you disconnected both battery cables?