Truck runs great cold or hot. However if I have to break hard for any reason, it instantly starts idling rough, us lost of power and even stalls when in 1st gear.
Itll sometimes “reset” after 20-30 mins or a hard turn or just after turning off and letting it sit for a minute.


Spark plugs are newer.
Clean MAF sensor
new AIC
new spark plug cords
Timing belt is in great condition
compression in all 4 cylinders are good
fuel injectors are all powered, ran cleaner thru them also.

next I’m pulling the EGR to clean and check out.

recently install all new AC, started 5 days after, May or May not be connected.

Trying to find out what could be causing intermediate stalling and extreme rough idle.

 

Welcome to the forum

What year Ranger?

Manual or automatic?

Does anything change if you select OFF in the Climate control?
Thats the only setting that AC Compressor doesn't cycle on and off

Could be the AC Compressor is enough of a drain on the engine to cause the symptom of an older problem you just did know you had until it was working again

Computer should bump up idle each time AC Compressor comes ON, if that doesn't happen then engine can stall and run rough.
How it detects AC compressor on varies by year

When you brake or turn your foot is usually off the gas pedal so engine drops to idle and if AC Compressor comes on and computer doesn't bump up RPMs you have what you describe

 

It’s a 1994, 5 speed manual transmission
and the idle does not change enough to notice when AC is turned on or off.
There is no tachometer so exact rpms are not possible.

im going to test the MFS to see if it’s going bad even though I cleaned it, as it’s making a “bogging” noise when it’s running rough as if it’s fighting to pull enough air into the engine.

And it does seem to “appear or start” after I break, but then it stays and does not go away until the engine is turned off and allowed to sit for awhile.

 

So try driving with AC OFF, to see if thats even the right track


The computer should get 12volts on pin 54 when AC compressor comes on, and that should bump up the idle, not allow it to drop, easy to hear the difference



Power Brakes use engine vacuum, if Booster is leaking then you get a substantial vacuum drop when applying the brakes, which can cause your symptoms
Remove the booster's hose from the intake manifold
Suck on that hose, lol, simplest free way to test it, you should NOT be able to suck air out, its a sealed chamber with a one-way valve
If you can suck air out then there is a leak inside or in the hose

Another test is to start engine, then shut it off
Count to 5, then press brake pedal down 3 times, you should have "power assist" 3 times then brake pedal will get hard to press down, that means booster is holding vacuum, which it should

 

So I was able to do 2 drives with no AC. About the same results on both.

1st drive - ran great all the way until I exited the tollway and caught the red light at the intersection where I had to go from about 75-0 in a few hundred feet, then it began to run rough and had trouble coming out of 1st , but it the idle was not as rough as normal and it appeared to run fine out of 2nd gear.

2nd drive- rough idle appeared to “somewhat” come back when slowing from 75-45 to switch highways on the exit ramp. This time though, only really felt the increased vibration. No knocking noise, no loss of power and no real notice to the truck’s performance , except a slight vibration In the gear shaft.

Performed both test for brake vacuum and was not able to suck out any air, and only got 3 brakes in before the pedal became stiff.

AC being off appears to minimize the results to almost nothing but if you’re looking for it, it’s still barely there.

 

Sorry, should have tried this first.

When I turn the AC on, the engine bogs down and begins to idle rough, only after a few minutes does it level back out to normal idle, there is NO increase in RPMs at all,

 

4cyl engines do not idle well to begin with, its the 180deg between cylinder's firing that makes them vibrate at lower RPMs, not smooth like a V6(120deg) or V8(90deg)
So 4cyls usually are set with a higher idle RPM, even with manual trans I would expect minimum 750 warm idle, even 800

When engine is cold idle should be 1,100rpms or so and you shouldn't have an issue with AC on
If idle is not high when engine is cold then you have either an ECT sensor issue or IAC(idle air control) valve issue

After engine is warmed up test new IAC Valve
Let engine idle and unplug the 2 wire connector on IAC Valve
RPMs should drop and engine may even stall, either is good it means IAC Valve was working, computer was setting idle RPMs
But computer is not getting the 12v "signal" from the Climate control when AC compressor is ON

ECT sensors can get "stuck" at a high resistance, so computer always "thinks" the engine is warmed up, if thats the case then you would not get the higher Cold Engine RPMs
If idle is higher on cold start then ECT sensor should be OK

 

Think I found the problem. The last jackass had it all wrapped up in electric tape instead of replacing it. This is the line that goes to the EGR (correction)


Ok, I will test both of these. The IAC valve is maybe a week old, replaced it 3 days after the AC as the idle was getting worse everyday.

still have to check the ECT.

 

"New" used to mean "tested and working"

New now means "YOU TEST IT, and we will replace it if it doesn't work"

We are the Quality Control Department, by our own choosing, lol, we want cheaper parts, and that means no testing before shipping

If you ever wondered why Motorcraft parts are so expensive thats one of the reasons, Ford still pays for the parts to be tested before shipping and human labor(even in China) is expensive.
But Ford can't afford to have a 20-30% failure rate in new parts, so worth it for them

They also require source of materials lists and labor documents so they don't get burned by using materials from forbidden countries or child labor law violations, Media loves to find those things, lol.

 

I learned that for sure.
I only buy motorcaft for my Ranger now.

When the IAC valve was unplugged, the rpms dropped noticeably but did not die. Also, the RPMs ramped back up once plugged back in. So IAC is working.

 

Picture is a Vacuum line, so not for ECT sensor?

 

Mistaken my acronyms.
ECT has not been checked yet. There are two so it’ll take to pull out both and test them.
Also, I assume that if one needs replaced, I should do both??

 

ECT sensor uses 5volts and wouldn't case stalling in most cases, it tells computer when engine is cold so it can run Choke mode, high idle/advance spark/rich fuel mix
Generally you just replace ECT sensor, but you can test it with ohm meter and a pan of cold and then hot water on the stove top

ECT SENDER uses 12volts and is for dash board temp gauge only so not involve with engine operation in any way

 

You can also check it on the vehicle by backprobing the sensor signal return to ground when the engine is cold, and again when the engine is hot.

I used to have a chart that showed the relative voltage to the degree the coolant was. I believe the CTS (coolant temp sensor, what you refer to as the ECT Sensor) is a min max range on most vehicles between 100/120 up to 260/300 degrees or so.

I believe the Ford system uses a 0-5V return, VS a 5-0V return, meaning 0V (or rather .1V) is engine cold or below minimum range and 4.9V is engine max range (overheated, at that point) A return of 0 or 5V is usually a failsafe that indicates sensor failure as the ecu needs some sort of feedback VS 0V feedback. Most systems are like this, with a rising voltage equivalent to a higher value.

Use voltage to scale readings. Until the temp sensor reads a level above its min "setpoint" the engine ECU logic assumes the engine is cold and runs in open loop (for the OP's knowledge)

 

Changes the IAC, cleaned the EGR and MFS and checked the ECT, all are either working or freshly cleaned and the truck seemed to slowing start work correctly for about 2-3 weeks as long as I did not break fast or down shifted while I was slowing.
However, now it is happening even when I merely let off the gas. As soon as the truck has even mild acceleration it’s starts idling rough. If I turn off the AC if is less but still there

 

ECT uses reverse of what you posted
.5v-.9v is warmed up, 190deg coolant
3volt is cold, 60deg or so

Chart here: http://www.fuelinjectedford.com/images/temperature.gif

Either the computer or the IAC Valve is the issue
With key on IAC Valves wires should show 12volts
The red wire should always be 12volts, battery voltage, key on engine off

The other wire, white/blue in 1994?
Is the control wire, its the Ground that comes from the computer, computer uses PWM(pulses) to lower and raise the voltage at the IAC Valve
So at idle you might see 8v-11v, remember the electric system is at 13.5v-14.5volts when engine is running, on these 2 wires
You can use sewing pins to test voltage