Hello,

I have a 1994 Ford ranger 2.3L that has been having an issue of wanting to die and then revving up the RPMs. At first I though this was only happening on cold starts but happened while in a drive through and fully warmed up. I will list all the parts I have replaced since this issue started Any help would be apricated.

List of items done so far:

1. Oil change
2. Spark plugs
3. Spark plug cables
4. Idle air control valve
5. Carbon canister to throttle body vacuum line
6. MAF cleaning
7. Coolant temp sensor
8. Alternator Serpentine belt

My thoughts are maybe an issue with the fuel system or possibly there is an issue with the cooling system since my temp gauge has been super low and the top rad line seems to not be taking in much coolant. I also think an o2 sensor could be replaced. At this point I feel like I am just replacing parts and guessing. Looking for any guidance on this issue.

 

Welcome to the forum

The computer controls the RPMs at idle
It uses the IAC Valve to do this, and its +/- 4rpm so pretty precise

IAC Valve should only be replaced with Motorcraft or Hitachi Brand, Ford uses true solenoid valves, other brands are stepper motor type like other car makers use

Lets first stop it from stalling from low RPMs
Warmed up engine, idling
Unplug the 2 wires on the IAC Valve
RPMs should drop to 600rpms, barely running, but engine shouldn't stall
If it stalls you need to adjust the Anti-diesel screw, looks like an idle screw
Its on the throttle linkage
Give it one full turn clockwise(tighten)
Restart engine IAC Valve still unplugged, CEL will be on
Engine should now idle barely
Put it in gear
If it stalls again do another 1/2 turn, repeat until it will idle in gear, barely idle, not stall
Put in park while still idling
Now plug back in IAC Valve and idle should go up to 750-800rpms on a 4cyl engine
Then unplug IAC again, rpms should drop but no stalling, if not back off the screw a bit, but just a bit


O2 sensors need to be changed at 100k miles or 12 years, not optional, and not your issue


On cold start the ECT sensor tells computer coolant temp with key on
If under 140dgF computer set Choke Mode, Richer fuel mix
Choke mode sets idle at 1,000-1,200rpms, depends on how cold
As coolant warms up idle will go down bit by bit
If that's not happening then change ECT sensor, its a 2 wire, 5volt sensor, might be on a heater hose on 1994 2.3l
Temp SENDER, for the dash board temp gauge, is 1 wire, 12volt, and on drivers side of engine toward the back by oil pressure sender
So did you change the 2 wire sensor?

2.3l Lima is a very heavy engine, built like a tank, so hard to keep it warm, radiator is never used in winter and barely used in summer, lol
But temp gauge should show above 1/3 once its warmed up, just below 1/2 is best
If not try this test
Start cold engine
Feel upper rad hose and heater hose, should be the same temp
Let engine idle for 2 min
Feel both hoses again, heater hose will be getting hotter, upper rad hose should still be COLD no circulation at all
If upper rad hose is warming up thermostat is bad or leaking, change it, spec is 195degF t-stat

And could be a computer issue, stalling is not really a computer issue but its free to have a look and good to unplug and plug back in the 60 pin connector, cleans the pins
In a 1994 computer is in engine bay drivers side down low between firewall and inner fender, follow the main wiring harness

Open up the computer and have a look inside, should look like this: http://www.kvitek.com/ford/img/ford_eec-iv.jpg
See the 3 Blue Capacitors, they leak after 20 years so need to be replaced, if you want to replace them just as general maintenance, do it, but check each out closely move with finger
Also clean off any corrosion anywhere on the board


When coming to a stop shift to Neutral, if there is no stalling ever then could be torque convert issue, its not unlocking like is should, extreme long shot

 

Thank you for your comment. I took your suggestion and warmed it up and unplugged the IAC. What this caused was lower rpms but with the same fade in and out. I took a video and will attach it below for you to hear the engine. Sorry its dark due to it being late here.

Video File: https://drive.google.com/file/d/12z8...ew?usp=sharing

 

Assuming new IAC Valve is motorcraft or hitachi brand.............otherwise you could be chasing your tail, or put the old factory one back on, since new one didn't help that much
Also unhook the battery, one cable, for 5min and reconnect, that will cause the computer to reset and relearn any new/changed devices, like IAC Valve

I would borrow or rent a fuel pressure tester and timing light

At idle fuel pressure should be steady between 30-35psi, but the steady part is the most important, even if its 25psi
There are two fuel lines coming into the engine bay from drivers side
One goes directly to Fuel rail feeding injectors, this is the IN from the filter/pump
The other goes to the FPR(fuel pressure regulator), this is the OUT(return) line back to the gas tank, looks like a small can
FPR will have a vacuum hose attached
Engine off
Remove vacuum hose, plug the hose
Start engine
Fuel pressure should now be 40-45psi and steady, again steady is the big thing, FPR is rated as 43psi when new so that's what you should see even on older ones, its just a spring valve
Also check vacuum hose for gasoline, FPRs can leak, and even a little gas being sucked in to intake changes idle
Steady fuel pressure is needed because computer calculates air/fuel mix on the fly, more fuel flows out of an injector at 40psi than at 20psi, so if pressure is not steady then RPMs can go up and down as computer tries to compensate for the more and less injector flow from unsteady pressure


1994 2.3l uses an ICM(ignition control module) for spark, last year for this
ICM does RPM spark advance, like the old springs and weights did in a distributor
Which works fine for SLOW acceleration
But when you want to have faster acceleration you a "load advance" for spark, that's what Vacuum Advance was for on a distributor
ICM uses the SPOUT signal from the computer, computer has access to the Throttle sensor, and air/fuel mix ratio needed when accelerating faster, i.e "foot to the floor", lol
With a Timing light at idle you should see a steady spark pulse at about 20deg BTDC
Do test with IAC valve plugged in
See if spark changes just before RPM changes, or is a reaction to RPM change, which would be normal
You are testing to see if spark timing is causing the drop in RPM, so timing changes FIRST which causes the RPM change

 

I wanted to update everyone on the progress: I went to the local auto parts store and loaned out a fuel pressure kit. While using the kit I noticed that when the fuel pump would prime the pressure would remain at 0. While running the engine the pressure would bounce rapidly with the engine from 30-45 PSI. I went ahead and replaced the fuel pump and this so far seems to have fixed my cold start idle issue. I will post an update to this thread if the issue returns.

Thank you all for the help with this.