It's been a long time since I replaced injectors, but as I remember there is a rubber seal, then a plastic holder, then a rubber 0-ring. I think I replaced both rubber pieces, reusing the plastic holder, which seemed fine.

If you are pulling the injectors, which seems like a good first fix attempt if spraying around them definitely causes changes in the idle, then you might try to move the hard fuel lines around, and hook up the injectors outside the engine, where you can check for leakage. Just turn on the pump for a few seconds and see if one drips gas. Obviously use precautions like a cool engine, fire extinguisher handy, etc.

So, it seems the idle starts out okay, then goes so lean the EHA can't compensate, then catches and goes back to normal.
Can't come up with a way an idle leak could cycle like that. And since pulling the EHA allows it to still happen, but not heal, then maybe it's a fuel delivery problem in the fuel distributor. Maybe a leak around the air valve piston that leaks down to a certain point, then the engine tries to recover and opens the IAC further, forcing the air valve to change position and clear it up awhile, then it starts all over again.

Just guessing of course, but it might point to trying to measure the EHA current as the cycle happens, and also measuring the low=side pressure to see if it drops during the go-lean cycle.

DG