I recently did a tune up on my IROC TPI 305.

When I pulled the plugs the left hand side of the motor was running lean and the right hand side was running rich.

Has anyone incountered this issue, and if so how did u diagnose the problem.

 

Lean and rich by how much?
I'd check to see if the injectors are firing properly and that nothing is shorted out.

 

If all of the plugs in a bank are running lean and the other rich, the problem is in the rail, regulator, or return line. Take the rail off and clean everything out and try replacing the regulator diaphragm and such. Does the car run as it should? No loss in power?

 

the only issue with the car right now is back firing when im downshifting. but no power loss, as far as im concernd its running great, i wouldn't have noticed till i did the tune up