The dirty side/clean side could just be PCV valve and Vent hose related.
One valve cover will have the PCV valve pulling in blow-by and oil vapor, the other will have fresh air coming in from air cleaner.
You could have a leaking injector, if engine sits over night leaked fuel evaporates, if it sits a shorter time start up is flooded by extra fuel in the intake.
You could get a fuel pressure gauge and test if system holds pressure when shut off.
Or there is a "clear flooded engine" routine in all fuel injection computers.
To start the routine:
Turn key on(RUN)
Press gas pedal to the floor and hold it there
Turn key to START
Engine should just crank and not start, if you release the gas pedal engine will start.
How it works:
With key on engine off, computer is on
When you press the gas pedal to the floor the TPS(throttle position sensor) sends the computer above 4.5volts, WOT(wide open throttle)
Since engine is off(no CKP sensor signal) the computer starts "clear flooded engine" routine.
This routine prevents fuel injectors from being pulsed(opened), so no fuel should flow to intake.
But spark will still be working.
So if spark is working but no fuel there should be a no start, if there is a leaking injector or FPR(fuel pressure regulator) then engine would start or at least fire a few times.
I would do this test after engine is warmed up, so do the test at the same time you notice the problem of the rich mix.
Wouldn't be code 86, that's a transmission code, shift solenoid.
The computer does have a wire spliced into the fuel pump power wire, this allows computer to "see" if fuel pump is getting power when computer turns on the Fuel Pump relay, if it isn't "seeing" the power, that could come up as code 87
That could be a failing Fuel Pump relay, which is common on older rangers, they are about $8 to replace, so almost a why not maintenance item
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