1990, 2.2, 126000 miles, AT, non-factory AC. Car has a pinging problem under load. No codes. Went to higher grade fuel, no luck. Changed plugs, no luck. Replace o2 sensor (had orginial) no luck. Did find a blown TBI to manifold gasket during a extensive vaccuum check, fixed it. Pinging problem not as bad. It will not ping when power braking in drive. I suspect now that timing chain/gears/tensioner need replacing. Car has DIS so I can't play with the timing. Car runs fine 'cept for the pinging issue. Plug read shows very good burn, light brown on all 4. Compression even across the board.
I would look into getting the timiing chain replaced, Sort of a pain in the butt to do, Its not to bad of a job. I had them same problem with one of my 2.2L corsica, I end up changing the timing chain as well, It corrected the problem, I also did a psi test on my fuel pump was getting weak as well, And added a new fuel filter.