1999 F53 No codes stored?

Has anyone else ever encountered no codes stored? I am a former ASE master tech and California smog tech back in the 1990's, things have changed and I need to isolate the component failure.

I own a 1999 motorhome on a Ford F53 Chassis. I recently had a few hints of an unstable idle, going up and down a bit and almost dying, I held the RPM's about 1,000 for about 30 seconds, and all seemed fine and I drove it. It ran great on a 30 mile drive with a few good hills and pulled hard @ 4600 RPM's up a hill running as good or better than it ever has. 3 days later I needed to return home and it tried to fire on cranking and wouldn't light all 10 holes. I could see black exhaust exiting the tailpipe. My scanner didn't pick up any stored codes and I finally was able to start it for about a minute but only by holding the revs to about 3500, then it seemed to shut off. I pulled the cover and looked around and didn't really find anything wrong with vacuum hoses or wires. I could not get it to start and idle and called for a tow, luckily I have good towing INS!

I got it home and it's still doing the same so I need a way to diagnose this, Does anyone have suggestions on where to start? I did remove the IAC and it looks like a small gap where it should be seated, WHen it fired again at home I couldn't feel the IAC working and when removed a second time it seemed to be in the same position. I'm unsure if the IAC would cause a full rich or over fulling condition, but maybe?

 

I was able to start it and run for about a minute by giving it more throttle and holding it at about 3000 RPM's, and the exhaust was dark, indicating it's fat and over-fueling. If I let the RPM drop it then became rough and wanted to die unless the revs increased, then after about a minute, it shut down on its own as if some electrical signal said stop. I don't think the fuel pump is shutting off as it's nearly new with less than a thousand miles on it since being replaced in 2019. I will plug in my fuel pressure gauge to confirm.

Does this sound familiar to anyone?

Oh boy, big tow truck!
Id probably want to know if it's holding fuel pressure. Been a while since I've seen it, but that's old enough to have a mechanical return fuel system. Possible that the pressure regulator is leaking into the vacuum line.
Otherwise I'd want to verify PCM inputs like temp sensors, oxygen sensors etc are not lying and causing over fueling.