Fast Idle and running hot

[mes64]

My 4.0l 94 ranger scab 4x2 automatic has developed a fast idle and is running very hot.I've gone through the motions of checking for vacume leaks and cleaned the mas and the iac to no avail.When shifted into park or neutral the engine idles up and down a few times then settles down somewhat.Very frustrating,just rebuilt the tranny last week and am hoping that I didn't wast my money.Hope someone can help.180,000miles no check eng light

 

[RonD]

First with engine warmed up and idling, unplug the IAC valve.
Idle should drop to about 500rpm, or below and stall, if so then IAC is working and computer is setting the idle high for some reason.
If idle doesn't change then IAC is closed all the way, so computer can not set idle any lower, the IAC valve is it's only control for idle.


Running warmer could be a Lean condition, lean fuel/air = hotter cylinders = hotter coolant.

But I don't think your issues are related.

Could be a stuck t-stat, when was it changed last?

Heater core on the '94 4.0l is the cooling system by pass, if it starts getting clogged up temp gauge will go up and down.
Hows the heat inside the cab, hot or luke warm?

Pop off the rad cap when engine is cold look at where the coolant level is, should be right at the top.
Start up the engine, if coolant comes out you could have a head gasket issue, there is no pressure in a cold system.
Let engine idle and warm up, idle should be 1,000rpms at this time, and should start dropping as engine warms up.
You can feel the upper rad hose and it should stay cold until t-stat opens, at about 195degF, 1/4 on the gauge
You should then see coolant circulating in the rad cap opening, if upper hose gets hot but coolant in rad doesn't then rad is clogged up.

 

[mes64]

the temp inside the cab is blazing,Bought the truck two years ago,no problems till now.I'll check the heater core for obstructions and watch the coolant level as well.seems to me that I had this problem when I first bought this truck and the guy I bought it from put a different mas sensor on it and it went away(hard start)would a bad egr cause this and will the truck store codes for these bad sensors even though no check eng light has ever come on?

 

[RonD]

Yes, the PCM(computer) stores codes where the incorrect data that set the code didn't last long, CEL never comes on for those.

EGR that is not working, valve not opening, would causing pinging under load and pinging causes running hot.
EGR valve that is not closing causes missing at idle.

You can unplug the MAF sensor(engine already warmed up) and see if engine idles normally, with MAF unplugged CEL light should come on.
While MAF is unplugged PCM is in Open Loop, so it runs preset fuel/air mix.

 

[canyoncritter]

fordfuelinjection.com will teach you how to pull the codes and give you the code list and tips on how to check for what on some problems

 

[RonD]

Oh and I forgot, codes don't mean a sensors is bad, a code means data from a sensor is out of it's preset range, so the computer is telling you where to look.

Example: code might show O2 sensor says bank1 is too lean.
This doesn't mean O2 sensors is bad, quite the opposite, if it reported this.
It usually means you have a vacuum leak and computer can't run rich enough to compensate for it.

A bad sensor often won't set a code because it......well, it is bad.
Example: engine misses now and then, and seems like it lacks power.
Could be a failing O2 sensor, it shows "normal" fuel/air mix when in fact mix is too lean, so it is a bad sensor causing the problem.


Anyway point is that you NEVER replace sensors, you test sensors with a $10 volt/ohm meter

 

[mes64]

I,ve been out in this lovely Michigan weather and did a koer test and the codes I received were 12 53 64 12 is a isc,53 is tps to high and64 is iat signal to low?

 

[RonD]

12 Idle Speed Control motor not controlling idle properly

53 Throttle Position sensor too high - TPS

64 Intake Air Temperature (IAT) signal low or grounded.


64 first, get a volt meter and a couple of sewing pins and test the sensor.
Sew pins are to pierce the wires to test voltage live.
My bet is a wire is shorted.
Read here for voltage you should expect:
http://oldfuelinjection.com/index.php?p=29

sensor is called IAT or ACT
Basically the computer sends this sensor 5 volts, as the temperature of this sensor goes up the voltage goes down.

TPS can be tested the same way, the 53 code.
Computer sends this sensor 5 volts, when throttle plate is closed computer should get .9 volts back, when throttle plate is wide open, computer should get 4.9volts back.
So as the throttle plate opens voltage should steadily increase from 1 volt to 5 volts.


12, IAC valve, remove connector and test ohms, should get 7-13 ohms, because there is a diode inside if you don't get a reading reverse red and black probes as the ohm test will only work in one direction.

 

[mes64]

you have been a great help ron!thx