1993 Previa. Fuel floods the cylinders after long drive & parked

no
more likely a hydraulic lock from excessive fuel on a piston cause by leaking injector /seal
remove the plugs and see if the engine will then turn over after it sprays the fuel out of the problem cylinder
vapor locks occur in fuel lines where the fuel boils off filling the line with air and locks the fuel by not allowing flow in the line

Follow top radiator hose or tube to engine ,Thermostate will be right there in housing.

There is in most cases only one reason for this and that is that the engine cylinder head gasket is leaking between the 2 cylinders.

Check the PND (Park Neutral Drive Safety Switch)

Hello. Welcome to FixYa.

The easiest way to remove the cylinder head is to lower the engine/transmission combination out thru the bottom of the vehicle; ie support the engine/trans, and raise the vehicle off of the powertrain assembly.

Working on the cylinder head whilst the engine is still in the vehicle is a VERY difficult endeavour.

Even though it looks like more work, by lowering the engine out; it proves much easier to work on and access all of the necessary bolts.

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first, the 1993 cadillac deville should have a throttle body not a carburetor. And, I think it has ported fuel injection to each cylinder with a fuel injector for each cylinder if it's like my 1990 Cadillac Deville.

Is it a vortec engine if it is your fuel injector may be the problem. Chevy ran one injector on the vortech engine it is under the upper intake manifold, it has 6 plastic hoses running to each cylinder under the manifold. if one of these hoses are leaking its dumping raw fuel into the manifold during hot soak. that fuel is getting picked up by intake air when trying to start. and flooding it out hence hard to start. gasoline evaporates rather quick so what fuel was in the manifold when you park for the night has evaporated by the next morning so no raw fuel for intake air to pick up easy start. Seen this problem many times. pretty easy fix but a bit pricey around $200

Does it spin at all? If not either the starter is bad or the engine is seized. Try to turn engine with a socket wrench on the crank pulley bolt. Anything happen to the truck just before you had starting problems (drive through a deep puddle, overheat the engine, lose oil pressure, blown head gasket)? If it was deep water the engine could have hydraulic lock from water in the cylinder(s), remove the spark plugs and try to turn it over with the starter. If it turns over clean, dry and re-install the plugs. If it overheated, ran with low oil pressure, or the oil was contaminated with coolant the engine is probably seized.