1989 302 engine mysteriously missing at all speeds, why?

Engine is in a 1989 E150 Van,  and the engine has suddenly began to  miss at all speeds, especial noticeable at idol. Feels like one or more cylinders are out. Hesitates on acceleration from idol and sometimes, backfires on acceleration.
when driven the miss is most noticeable,  engine  lacks get up and go and hesitates on acceleration engine shakes violently.

Slight throttle will not move van.

Engine fires up but idols very rough. stalls several times unless accelerator is worked regularly.  will not idol on its own until well warmed up.  when warmed up and idling, engine begins to die, nearly stalling.... but recovers on its own

I have changed the idol air sensor located on the air manifold., two years ago... Could it be bad already?....how do I check for it to be bad?

I checked the throttle sensor with multi -meter, and it is good. Engine Has clean air filter, new fuel filter, new plugs and 8mm wires.

using a stethoscope probe, I can hear each injector clicking as engine runs.
I added 24 oz of injector cleaner to 8 gallons of fuel, and still have engine troubles.

I find no vacuum hose leaks, no cracked hoses.

Plugs all have nice slightly tan porcelain tips.

I see No ' fireworks show' from the plug wires  at night .

Engine has 108,000 miles.
This 302 has fuel injection.
fuel pump pressure is 41 lbs.  with engine off and engine running. pressure drops at idol to 35 lbs.  when engine begins to stall, pressure drops then recovers to 41 lbs. then returns to 35 lbs.  

The fuel rail regulator is vacuum controlled.  I have vacuum at the regulator.  When  I disconnect the vacuum hose from the fuel pressure regulator pressure goes to 41 lbs, and  engine still  revs up and down at idle ...
Have not checked timing because this  requires a magnetic induction type timing light, which I do not have. ...maybe I can rent one from Auto zone?

I checked EGR valve operation with vacuum pump, and it holds vacuum and moves freely, I can hear  the EGR  clicking. With engine running I applied vacuum o EGR and  engine almost stalled. So it is working.
There is  No restriction in exhaust converter.

There are no trouble codes that have set, parts store's code reader/tester found there to be none.

So what is wrong / broken with this 302 engine of mine?...help!