4.0 Idle Issue

[C.Fuller305]

I have a 1994 Ford Ranger 4.0 V6 4X4 with the M5R1 Transmission. When I idle for long periods of time like sitting in a drive through my truck will cut off, also when I start it up in the morning after it has sat for a few hours I have to keep my foot on the gas for it to warm up because it will jump from 750 rpm to 2000 ish rpm then shut off. Just so everyone knows what has been done to it. New fuel pump, fuel filter, fuel pressure regulator, spark plugs, wires, MAF, O2 (2 of them), MAF wire plug, new ecu (yes the 200+ dollar computer is new), Head gaskets and up, air filter, Idle Air Control Valve is new, belt, idler and tensioner pulley. That is all that has been done to the engine all of my fuses and relays are good and have been double checked, however I do not have an EGR valve I'm not sure if it wasn't included from factory or if a previous owner removed it. the only thing that isn't exactly how it came from factory is my fuel pump relay the fuse box was giving me problems so I had to remove the wires and hook them straight onto the relay. They are in the correct order and each wire has shrink wrap and electrical tape to prevent a short.

 

[C.Fuller305]

Does anyone have any suggestions because I am lost trying to figure this out

 

[RonD]

Two suggestions
New ECT sensor, it sets Choke and also sets warm engine idle, its a 2 wire 5volt sensor near thermostat housing on lower intake

The 1 wire unit that looks similar is 12volt temp Sender used only by dash board temp gauge


Second is to pull out the computer and change the 3 capacitors on the circuit board
Its down low on drivers side of engine bay, between inner fender and firewall, bit of a pain to get out

These 3 capacitors are easy to see, usually blue cylinders, they leak after 20+ years and cause odd issues
Take pictures to get values from each and direction they face, they have a + and - orientation
Replacements are under $3
Not hard to remove and install or get a friend that can solder to do it
You should replace them regardless

They have a value like 16uF and a voltage like 50v
You need to replace with 16uF but it can be a Higher voltage, like 16uF 100v, but NOT a lower voltage like 16uF 16v

Also clean up circuit board, it does have a coating over it but some expose areas can get corrosion

Unplugging the main connector and plugging it back in also CLEANS all the pins and slot in case some were questionable
All the sensors use 5volts and the O2s use 0.1 to 0.9 volt, so any bit of a poor connection can cause bigger issues

 

[C.Fuller305]

Two suggestions
New ECT sensor, it sets Choke and also sets warm engine idle, its a 2 wire 5volt sensor near thermostat housing on lower intake

The 1 wire unit that looks similar is 12volt temp Sender used only by dash board temp gauge


Second is to pull out the computer and change the 3 capacitors on the circuit board
Its down low on drivers side of engine bay, between inner fender and firewall, bit of a pain to get out

These 3 capacitors are easy to see, usually blue cylinders, they leak after 20+ years and cause odd issues
Take pictures to get values from each and direction they face, they have a + and - orientation
Replacements are under $3
Not hard to remove and install or get a friend that can solder to do it
You should replace them regardless

They have a value like 16uF and a voltage like 50v
You need to replace with 16uF but it can be a Higher voltage, like 16uF 100v, but NOT a lower voltage like 16uF 16v

Also clean up circuit board, it does have a coating over it but some expose areas can get corrosion

Unplugging the main connector and plugging it back in also CLEANS all the pins and slot in case some were questionable
All the sensors use 5volts and the O2s use 0.1 to 0.9 volt, so any bit of a poor connection can cause bigger issues

So I replaced the ECT sensor and it does seem to help a lot I left it idling for about 15 minutes never cut off so I am waiting for it to cool down and try a cold start to see if that issues is resolved also I don’t want to mess with the computer (ECM) at all for the sole fact of it is less than four months old I had ordered one and replaced it because my old one had burn marks on it

 

[RonD]

Rebuilt computer will have the new capacitors already, thats about the only parts that are changed to get the "rebuilt" status