87 305 tbi idle issues

I installed a complete tbi , 305. Turbo 400 from a Chevy g20 van. I replaced all sensors and bought a rebuilt throttle body. I used the existing wiring harness fuel tank and pump from the van. Starts cold in closed loop and idles at 1200 rpm. Warms up and drops to near 700 rpm. After I drive it the idle is unsteady and often goes to 500 rpm. When I turn on the AC the idle increases nicely.
I purchased a refurbished ecm but the problem got worse. Now the idle is too low to start it and the AC idle control no longer works so if you can get it running and turn on the AC, it quits. Did I get a faulty ecm, maybe? PROM is adtj.
Comments and suggestions are appreciated.