Hello, my 1991 Z28 has been idling very rough lately. I changed the spark plugs, plugs wires, distributor cap and rotor, and the coil, and its still idling very rough, it even cut off on me at a stop light. If anybody has any idea what might be causing this problem, please respond. Thank you.

Perform a power balance test of the injectors. The test can be done with only a tachometer (NOT the in-dash tach) and no other tools.

could you explain more?

Well I had a similiar problem. Did everything you did with the same result. Ohm'd my injectors and found one dead. Replaced it, put new plenum gaskets on, cleaned all the manifold / tpi / egr passages, etc. and boy it runs super smooth and fast now.

Just my 2 cents...