2000 3.0 with around 134k miles. The car has been starting without an issue. The a/c is out so I hooked the gauges up to see where I was on the 132 since the clutch on the compressor was not coming on. In the mean time I also swapped the Throttle control relay with the clutch relay just for a relay swap.

I went to start the car and the idle went nasty between 400-1,200 rpms then died. It did this a couple of times. Now it won't start at all. It turns over but doesn't run.

Relays have been returned to original location
I have spark
Plugs are good
Pressure in the fuel rail
Good relays and fuses
Good battery
Car will not run on carb spray so I ruled out fuel issue. The engine will run for 1 second with carb spray (yes I am not spraying the MAS) but refuses to run.
No DTCs

... and no warning. Anyone have an idea where to go?

 

I'm guessing either you disturbed something (causing vacuum leak or a chafed wire to short or a poor connector to quit or ...) or a sensor chose that moment to go bad. Would have to be a critical one such as CKP or ECT.

Worth checking no damp/water in trunk, too.

If I were guessing a sensor it would be CKP. (If you can, scope it.)

 

I've gone over everything I touched, not much of anything, and I don't see anywhere where I jostled or chaffed anything.

I think the CKP is a good guess given that they fail and don't give a trouble code warning. But, I would have expected it to show symptoms of pending failure.

I will check it out in the morning.

In the meantime, does anyone else have a suggestion?

 

Confirmed that it is not the CKP

 

There's a lot still to check. If you need inspiration there are lengthy previous threads with details and pointers to step-by-step PDFs.