Failed smog, running very rich. changed plugs, cap rotor, wires, tps sensor, map sensor, egr valve cleaned, Has problem keeping stable ide. all over the place. Any ideas

My truck (92 with a 5.0) acted similar. It ran bad, hesitant, and very rich and my check engine light came on. It turned out being the fuel regulator. A bunch of sensors came up as bad on the computer test but i never changed any of them. Regulators are usually cheap. Hope this helps!

I've seen two cases recently where it was bad distributors causing rough idle. An honorable muffler shop (not a big chain) will test your catalytic converter for free. Is a '91 throttle body? Do Fords have cold start valve or injector? This can cause rich reading if malfunctioning. Anything controlling fuel delivery into engine can malfunction sending extra fuel. When you find problem; do you know clean oil will help pass smog test?