My camaro has really low RPM when timed "properly" - 6-8 degrees BTDC, and even with the throttle screw far out. My ECM isn't giving any problem codes, but the air pump is shooting air to the outside. I have an issue with a rich mixture and backfiring, but backfiring only occurs when I hit the gas pedal hard.
Things I have done...

New spark plugs and wires
New Throttle Position Sensor
New Idle Air Control Valve

Another thing. The car seems to run better (smoother and not so rich) when the timing is advanced farther before top dead center, like 6 - 10 more degrees. Then it still has a slight hesitation on the acceleration, but hardly ever backfires. Also, I read somewhere about how the car's RPM should drop when it's put into gear. Mine does drop, somewhere around max of 100 RPM

1986 Z28 Camaro
LB9 - tuned port injection (fuel injected)
305

Any ideas on what I should check or look for next?

 

its possible that the outer ring on the damper slipped a little and it throwing you off on your timming, you could pull the #1 spark plug and turn the motor until the piston is at the top of the stroke, then look at you balancer and see if the mark is somewhere near the pointer.

 

I checked the piston position by pulling the number one spark plug and making sure it was at/near the top of the cycle. Good idea and keep them coming...