2000 Ranger 4.0, 5-speed will not idle smoothly, and stalls out

[cargoflyr69]

Having issues with engine running like crap at idle speeds. Sometimes will stall if you don't keep your foot on the accelerator and running 1,500ish rpms at the stoplight. Was throwing generic CEL codes for "too lean bank 1" and "too lean bank 2"

Suspected vac leak somewhere, Investigated by spraying starting fluid around the engine bay, near intake manifold and other vac related accessories. No change in RPM. I did swap out the Idle Air Control and the idle got a bit better but not fixed. Got some advice to change the Mass Air Flow sensor. Did so with no change or improvement.

I then disconnected the the MAF sensor at the harness and mysteriously the engine idle smoothed out and basically ran perfectly. I took a 10 min drive and got up to highway speed and a stoplight. The idle problem seems to be gone, but the MAF is still disconnected. When I got home, sitting in the garage with perfect Idle, I plugged in the MAF sensor and the idle instantly went to sh*t. I had to work today, so drove it in with the MAF harness disconnected and other than a slight hesitation when initially accelerating, there were no issues at all on the drive in.

I'm baffled.... What could be going on here? Thank you in advance!

 

[RonD]

Welcome to TRS

Is the new MAF sensor Motorcraft brand?

If not clean the old one and put it back on, see what happens

There are some parts that 3rd party brands don't do well with, either bad out of the box or fail after a few months
MAF sensor, IAC Valve and Fuel Pump are three of those parts
Hitachi brand seems to be best 3rd party if you can't get Motorcraft

So I would suspect the new MAF sensor, and keep an eye on the IAC Valve if its not Hitachi or Motorcraft

MAF sensor should have 4 wires, test the red and black wires for 12v/ground, that's the heater for MAF sensor, should show battery voltage with key on

When MAF is unplugged the PCM(computer) uses data tables in memory to "guess" at correct air weight/flow, so MAF is most likely not sending valid weight/flow or its sensor wires are corroded so PCM is not getting correct data from MAF
MAF is used for best MPG so engine is just running a little richer than needed, but OK to drive

You should also now have a Code or codes indicating a problem with MAF sensor, since its unplugged, if not then could be a PCM problem

After engine is warmed up and idling
Unplug the 2 wire connector on IAC Valve, it will close
Idle should drop down to 500rpms or engine may even stall, either is GOOD it means no vacuum leaks
If idle doesn't drop then there is a leak somewhere

 

[cargoflyr69]

The IAC is Motorcraft. The MAF is 3rd party. Are you suggesting this piece may have been bad out of the box? How can I troubleshoot the sensor itself? The 3rd party MAF was about $125 and Motorcraft was $520!!!

I will check the red and black wires on the the harness for correct voltage/ground. Is there anything to look at with the other wires in that harness?

How to troubleshoot the PCM computer? Is there a hard reset? did it perhaps "learn" before I swapped the sensors? I did drive about 1,000 miles with this idle condition. Would the PCM unlearn, or is this theory not a thing?

Thanks again!

 

[RonD]

Wrecking yard Motorcraft MAF is better than any new 3rd party MAF, these just don't fail that often, but rarely is not never
So used is not a big gamble just clean it

Motorcraft parts are expensive because each one is tested before being shipped, labor to test is expensive, especially since those pesky child labor rules came around, lol, and of course new minimum wage laws to avoid the whole "sweat shop" labeling that big companies like Ford try to avoid

For 3rd party YOU are the tester, they provide a warranty as the Quality Control, you test it, if it doesn't work they replace it
And this is great for most parts, as long as they are easy to swap out, why not save the money
But never "trust" them, or you can end up chasing your tail around thinking "well its new so that can't be the problem"

Test seen here: https://www.therangerstation.com/tech_library/CleanMAF.shtml

About half way down, these are running engine tests
A and B are the heater wires
C and D are the sensor wires

Use a couple of sewing needles to pierce the wires to get voltage reading if you probes can't get into the connector when it plugged in

Sensor has lower voltage at idle then it goes higher as RPMs go up