FYI: valve responsible for bad warm restart

I notice that bad warm restarts are sometimes hard to figure out on these trucks, so maybe this will help someone.

I just had that today. Restarted warm and it didn't get going and died. Same thing until I held down the gas pedal a little when starting and kept it on for a moment. It felt like a clogged IAC valve, but I ripped it all apart and found it to be clean, opening to voltage, and good resistance.

It turned out that I had left the fuel pressure regulator vacuum switching valve (the brown valve behind the engine) unplugged! It was days ago and it didn't have a critical effect until today. I have noticed this ECU is fairly stupid, having no idea this was happening, nor about other airflow issues like all the EGR components and IAC. So if something is clogged or inoperative, you wouldn't know unless you fully check it out.