Sorry I don't know what an LS is, I guess from the cam belt comment it's not a 2.0TS but a V6 of some sort.
For a 3.0V6 24V, Error Code 1-2-2-1 = Air flow meter faulty (probably)
There is a list of codes here:
You do sound like you know what you're doing. If this IS for your car, I would look at anything to do with the air flow from the airfilter right to the throttle body, check for blocked airflow at the airfilter or cracks in the AFM/throttle body pipe, look for free movement in the AFM flap itself, you can clean this with proprietary cleaners but obviously don't damage the internals, check the electrical connectors to the AFM and any other airflow components.
If you can get the engine to run, grab the AFM and push it up and down real hard, visibly bending the corrugated plastic air pipe. Any cracks will change in size and the engine revs will change as a result. Also pull off the top of the airfilter cover and see if that makes any difference to the revs or indeed the starting. It might let air in if there's a filter or intake blockage.
Check the integrity of those two pipes that run back to the plenum from the AFM pipe too.
It can be an erroneous error code, that does happen sometimes. If the airflow system is all good then I would agree that the ECU should be looked at and cleaning the connectors is always a good starting point as already mentioned earlier in this thread and at the same time the ECU relay operation.
Keep us posted with the results. Good luck!