97 SC2 engine woes...

My daughter has a 97 SC2. Here is a brief history, followed by my problem. Car was bought with 80,000 miles. Drove nice, engine good, trans shifted nice (5 speed). Then, for reasons unknown, engine threw a rod. I located a 97 51,000 mile engine, daughter made some contacts and a shop installed the engine, a new clutch and slave cylinder. Now for the present. Engine has been misfiring and giving these codes. P0300-Random/multiple cylinder misfire detected, P0134-O2 sensor circuit no activity detected (bank 1 sensor 1) and also P1133-HO2S insufficient switching sensor 1/bank 1 fuel control shifted lean (faosc). Now, I have taken it to a local mechanic (non-Saturn) and he can't find anything. The car has new plugs (NON-platinum AC Delcos gapped correctly), new coil packs, new ECTS, new O2 manifold sensor, new silicone wires, new valve cover gaskets. The newest plugs and valve cover gaskets are my recent additions just before she went back to college. She "thinks" it is not missing anymore, but not sure and time will tell. I told her to have the codes reset and keep me informed.
Is there anything I've missed? Mechanic says the MAP and everthing else he has checked looks right to him. The engine was running rich before the plug/gasket change. I'm open to any and all advice. I have a 1965 Mustang and that's pretty much where my knowledge lies.....NOT in Saturns. Thanks in advance.

Try closing the gap on the plugs to .025 - .028

Sometimes that helps.

Don

Try closing the gap on the plugs to .025 - .028
Don

not a very good idea.

I would try the ignition module common problem with that vehicle. Also you may want to remove the ac plugs and go back to oem saturn plugs.

Always keep the gap on your spark plugs to manf spec. .040 is the spec on your engine. Get the the mechanic to hook up the scan tool to your car and look at the coolant temp sensor readings. The temp sensor are known to crack on your style engine witch would give false reading to your pcm, messing up your air fuel mixture (ethier to lean or rich) Make sure they remove it to examine it. There is a new design, the old 1 is made out of ceramic and the new design is made out of brass