1992 Oldsmobile Delta 88 Unsolvable problem?

Hi and thanx for taking the time to read this, the problem is its runs horribly rough on idle and backfires with acceleration also noticable power loss now list of new parts include, IAC, MAF, O2 Sensor, coil pack, ignition module, 2 sets of plugs and wires, ecm, front exaust manifold, vaccum test, fuel pressure test and everything is ok. No check engine light, node light tested, tested intake multiple times with multiples substances was ok still can't find the the problem. Had it on the snap on scanner everything read ok accept the rich/lean was always cean and in closed loop rev it up and open loop would kick in. This car is great cruising down the highway, all the valves are good. I dunno i'm stuck on this one hoping someone may have a good suggestion. Oh and its definately not the cam or crank sensor lol new