Engine stumble when coming to a stop, while in gear.

[franklin2]

For this test, I have 8.8 ohms cold and 11.4 ohms at operating temperature. The meter was set on the 200 ohm setting. (I’m not really good with electrical meter testing stuff, but I try to fumble through it)

i also tried unplugging it while it was running and it died immediately.

Dying immediately may mean the throttle stop is too far back, the butterfly is too closed. The rpm with the IAC unplugged varied from engine to engine, but I have found it seems to work best when you unplug the IAC the engine keeps going, but very slowly. What you can do is take a magic marker and mark where the throttle stop screw is located now, and then turn it in till the engine idles very slow with the IAC unplugged. Make sure the engine is fully warmed up before experimenting with it.

And I will tell you once you make this adjustment, it's going to take a couple of drive cycles before the computer relearns the new setting. This may help your dying problem, since the engine cannot completely die from the IAC if you set it to idle slowly with the IAC unplugged.

 

[AK Ranger]

I warmed the truck back up and adjusted the blade stop screw till the truck idled about 500-600 rpm's with the IAC unplugged. Took it out for a few short drives around the neighborhood and is is somewhat better, but still drops down to 500 rpm’s on occasion.

I don’t really want to go much past the 500-550 rpm range. Unless there is room for more.

Warmed up and in Park, it idles about 1000 rpm’s.

 

[AK Ranger]

New issue, might be related. The Check Engine Light came on. I scanned it and it is a P0122 TPS Code.


**EDIT**
Just got back from a little longer drive and if taking off from a stop and making a bit longer pull and then let off the throttle, it will drop to 500 rpm’s, then bounce up to 1200 rpm’s. It will do this a couple times, then settle down.

 

[franklin2]

It will take a few drives for it to settle down. Sounds like your IAC is a little slow. It cuts all the air off when decelerating, and then has to come back on quickly to maintain idle. As long as it doesn't stall, I would live with it for awhile. Don't open the throttle too much. If you do, you might get the TPS voltage over 1 volt at idle. That can be were the code is coming from. If you do not mind poking the wires or back probing the TPS connector, you can measure the voltage with the key on engine off, and see where you are at.

You can turn it back some, as long as it doesn't stall on you again.

 

[AK Ranger]

Awesome, thanks franklin2!

We’ll drive it around a bit more and see if it improves. I have heard/read about people cleaning and lubing the IAC. Is that’s really a thing?

 

[franklin2]

Yes, that and the throttle blade. When you turn the engine off hot, there is a wispy smoke that will come from the engine and it settles on these parts. Over time it turns into a black/brown sticky build-up that can clog things up.

If you find it really dirty and clean it, then your settings may be off. You may want to turn the screw back were it was when you started if this happens.

 

[AK Ranger]

Last night, I moved the throttle blade screw back to where it was, took it for a drive and still did the same thing. No measurable change.
I decided to take a chance and replace the IAC. No real change either. At this point, I plan on driving it, or should I say, have my son drive it.
We’ve been working on it for a bit now and it will be his first vehicle.

 

[Brain75]

how does the wiring around the TPS sensor look... since the ohms was good on the IAC valve, I am not surprised that replacing it had no change.... I like engine-codes better than any other site for OBD2 codes sine their troubleshooting seems spot on.

P0122:

P0122: Code Meaning, Causes, Symptoms, & Tech Notes

How to repair P0122 code Throttle Position Sensor 1 Circuit Low Voltage

www.engine-codes.com

Common Causes of P0122

A faulty Throttle Position Sensor (TPS)
Damaged wiring or connectors in the TPS circuit
Corrosion or poor connections in the TPS wiring harness
Issues with the ECM or other related components

3 out of 4 are TPS, so that would be my #1

 

[AK Ranger]

how does the wiring around the TPS sensor look... since the ohms was good on the IAC valve, I am not surprised that replacing it had no change.... I like engine-codes better than any other site for OBD2 codes sine their troubleshooting seems spot on

I actually thought my IAC ohms were way out of whack, so I took a chance.

The TPS wiring looks good, nothing of note.

The P0122 code came into play after I messes with the throttle body blades. Once it was cleared it never came back.

Not into snake oil, but I’ve had good luck with SeaFoam in the past, so I’ll give it a try tomorrow. The fuel tank has a can of fuel treatment in it now and I’ll fog the topside tomorrow.

 

[Brain75]

next up test the tps electrically.... where he says don't probe the hot lead with your meter to ohms (you will ruin your meter), I would add just shut the key off so no power. Kind of obvious when you think about it but just another extra step.
And unless my eyes deceive me, i see a Ford oval on the throttle body so the guy is demonstrating on a Ford even.

 

[AK Ranger]

next up test the tps electrically.... where he says don't probe the hot lead with your meter to ohms (you will ruin your meter), I would add just shut the key off so no power. Kind of obvious when you think about it but just another extra step.
And unless my eyes deceive me, i see a Ford oval on the throttle body so the guy is demonstrating on a Ford even.

So I did the test, the increase and decrease were smooth, no jumping around. Even with tapping on it.

Now, the base number was low, at 0.77 volts.

If it should be around 0.95 volts, it takes quite a bit of turning on the throttle blade screw.

Is it better to keep it low, or crank it up to what he had in the video?

 

[Brain75]

It should be as close to 1.0v as possible... but I read somewhere that anywhere between 0.5 and 5.0 are considered valid range. Based on that I would think this isn't the issue.

Do you have any confidence your tach is highly accurate? (mine isn't and Ford wasn't super precise - tend to read higher than real life) I ask because if you are actually really turning out 450 rpms and the gauge says 550 I could understand the stalling and sputtering.
I didn't figure out my tach was off until I drove exactly 75mph and noticed the rpms was just too high... started hunting for ways to get better mpg and figured out that the tach was lying.
Another thing I found in another thread apparently more an issue with 3.0 than others is they burn up the spark plugs... have you pulled a plug or 2 and checked how they look (mind the gap too).
An old thread but several points discussed are good info:

92 3.0 rough idle when cold

ok guys i just bought a 92 ranger and when you first start it up for the day it studders pretty bad but after 30 seconds to a minute it idles normal anybody got any ideas?

www.therangerstation.com

Another point I don't know the exact answer to is what should your idle RPM's be... the 3.0 is a higher rpm beast, it is just getting its legs at 3k - best fuel economy is actually above 3k I read. I saw over in ford-trucks a number of people saying cold idle is 1,100, and warm idle is 650 which would be exactly the same as my 2.9, but then others claim it was higher in later years too.

 

[Brain75]

another point on the IAC - you have replaced it right? did you disconnect the battery for 30 minutes to purge the computer of all learned IAC values?
After you do that (disconnect battery) it takes like 3 start/warm up to temp/shut off cycled before the idle will level out as the computer learns new IAC ranges.

 

[AK Ranger]

Funny thing, doing that now. It’s got 20 more minutes to go.

Yes, I did replace the IAC.

While it was heated up, I adjusted the throttle blades so the truck would run at about 450 rpm’s with the IAC unplugged.

Tomorrow and over the weekend, we’ll get some miles on the truck and see how it goes.

Not sure if it is related, but it definitely runs a bit rich. There is always black soot spatter coming out the tailpipe. It painted a spot on my garage wall… lol

 

[AK Ranger]

It drove okay, still had a few stumbles, but recovered. Will report back as we drove it and as it progresses.