If you live in an environment with salt-laden air, and the
starting problem only occurs when the humidity is high, then
wipe clean all high tension insulators (plugs, leads,
distributor cap, rotor).

John

If you have an old Fuel filter, it can cause intermittent flow of fuel.
Check your spark plug's gap, make sure they are even because your "Engine
Service"'s light is telling me that something was wrong with your combustion
previously, either you put the dirty fuel in or you made it produce too much
toxic gas with uneven gapping.  This problem could spread to damaging
distributor's contact(s).  Not saying they already happened, maybe....

This one seems like a serious problem.  In reading the other posts a
couple of comments come to mind:  Your location may not have salty air
but what about salty roads?  Where do  you spray the starting fluid?  If
 you spray any liquid at the air filter, the air liquid will stay
there.     Or do you mean you spray it in the housing, right by the MAF?
 You mentioned that the spark plugs and wires were changed in the past,
how long ago?  what about the distributor cap and rotor?

For a cranking car to start you need three things:  Air/Fuel mixture, a
source of ignition and an engine in acceptable mechanical conditions.
Even though your tests seem to indicate you have them all, by the car
not starting, it is obvioius you do not.  For a your car, the only
sensor that may prevent it from starting is the camshaft position sensor
inside the distributor.

To read the codes, you need a small flat screw driver, the ignition key
and the procedure that can be found on the service manuals that can be
found online for free.

I have a few questions:

Is yours a SR or a GA engine?

When the car does not start, after cranking, does the exhaust pipe smell
to unburnt fuel?

When the car finally comes on, does the engine run normally or it
stumbles and misses?

The procedure I would follow to diagnose this problem is:

Is there fuel pressure in the hoses leading to the fuel rail?  (does the
hose get hard when you turn the ignition key on?)

Can you start the engine when you depress and hold the gas pedal to the
floor, cranking the engine for 10 seconds at a time?

Mark the position rotational position of the distributor with respect to
the engine head so it can be put back together in the exact position it
was, remove the distributor but keep it connected.  With the ignition
key on, can you hear the fuel injectors click when rotating the
distributor shaft?

If you remove a high tension wire from a sparkplug, and with the use of
insulated pliers hold the tip of the wire (not the insulating boot, may
need to use a metal rod or similar object) at 1/4" from the tip of the
spark plug electrode, and crank the engine, can you see the spark jump?

Are the spark plugs fouled?

I hope this info helps.

Good luck!