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4.0l OHV(1990-2000) Rangers could leak coolant from top rear on Drivers side, lower intake manifold where it bolts to the head

Yes, could also be a Core Plug(freeze plug) has rusted thru, not uncommon on any 20+ year old engine
These can be replace with rubber expansion plugs of the correct size, easier to install than factory plugs

Engines REV up because of air flow, i.e. when you press down on the "gas" pedal you are letting more AIR into the engine not gasoline, should be called an "air" pedal, lol

So when any engine REVs up on its own............................................... ...AIR is getting in, often called a vacuum leak


On the upper intake manifold is the IAC Valve, pictures here: https://www.explorerforum.com/forums...-w-pics.84220/
Warm up the engine and let it idle
Unplug the 2 wire connector on IAC Valve, it should close
Idle should drop down to 500 or engine may even stall, either is GOOD, it means no vacuum leak, if RPMs stay high then you do have a leak

Its easy to clean the MAF sensor, also clean IAC Valve as well.

 

What condition is the coolant in the reservoir? Is it dirty and foamy?

Also, there are no such thing a "freeze plugs" or "frost plugs"
They are there to plug the holes used to remove the casting sand after an engine is cast.

 

This is true they are Core Plugs , but.............................most people call them Freeze Plugs which is fine, since there is no double meaning, and most would understand what you mean when you use "freeze plug" in a description, many less would understand what you mean by "Core Plug", lol, so the incorrect popular word, has overshadowed the correct word

i.e. Starter Solenoid
A Starter solenoid is ON the starter motor, it moves the starter Gear out to mesh with the ring gear when starter motor is activated
There has never been a starter "solenoid" on the inner fender of any vehicle.
That is the starter RELAY

A Solenoid causes MOVEMENT
A Relay makes an electrical connection
They both work the same way, and a "solenoid" was first to be developed, so became the go to name


The Freeze plug name came into use before there was Anti-freeze, people had to drain the water in the blocks if freezing temps were expected, all engines at the time had a drain plug or petcock so water could be drained out
If they didn't drain the water then the Core Plugs would be pushed out as the water froze and expanded inside the block, and no this wouldn't "save" the block from cracking in a hard freeze, that was a popular Myth, lol.

Any way the Freeze plug name stuck and its well over 100 years in use so.............there are such things as freeze plugs or frost plugs(never heard that one)

Its fine to offer up the Core Plug as an alternate name, I do all the time, but Freeze plug is fine to use as is Starter Solenoid(even though its NOT a solenoid, lol)