93 Ranger 4x4 4.0 High Idle / Drivability Problems

[Vincenthdfan]

I don't know if this relates to you but I'll just toss it in here. Replacing the IAC twice on this truck has helped, the original one was defective, the new one was defective, the third one seems to be okay although I still get a burst of high RPM (2300) when it first starts but it drops right down to 1000

I'm embarrassed but I'll be the first to admit I'm not always right about everything sometimes I'm not right about anything lol anyhow fussing around the truck today there is a hole in the throttle plate body!

I replaced my new IAC once already with another new one under warranty and experienced no change (but that's still not to say its any good either?) and I also have the original FOMOCO IAC that I have been periodically installing to test it out.

It does the same high revs when driving above 15 mph, albeit to a lesser degree/RPM.

The new Throttle Body helped immensely at sitting still idle, worked really well...now if I could just get it to settle down with IAC when driving??!!

 

[RonD]

The TPS doesn't set anything for the computer, its a "heads up" to add fuel quickly before higher air flow would register from MAF sensor.
So like the accelerator pump in a carb, you get instant acceleration if its working, no dead spot waiting for computer to see more air flowing thru MAF sensor.

When you take your foot off the gas pedal, TPS under 1 volt, computer WILL shut off fuel injectors until RPMs are under 1,500, then it will restart them at idle levels, this saves gas.
With a carb when you closed throttle plate vacuum in intake would go UP, and suck more fuel out of idler Jets than needed.

So coasting down hill in neutral saved fuel with carb engine
Coasting downhill in gear, above 1,500rpm, uses 0 fuel with fuel injection, it does squirt fuel now and then to keep Cats hot

So can't see TPS causing the issue of stalling, its not what it is used for

Computer sets fuel based on RPM and air flow, TPS position matters but only if it changes quickly, and computer does compare MAF air flow to TPS position, if they don't "match" it will set a code, i.e. computer "knows" how much air a 4 LITER engine will pull in at 50% throttle, its just math.


You should unplug IAC Valve after engine is warmed up and set the "anti-diesel" screw so engine will idle at 550-600rpm so it won't stall again.
Then plug IAC back in

 

[Vincenthdfan]

OK,
With the new IAC, new TPS, and new throttle body I can get her down to a nice, steady 600-650ish RPM.

However, unhooking TPS at idle makes zero difference...cant get it to go any lower than 600ish even with screw 100% lifted off the stop of the new throttle body.

I also found when driving it, its much more pleasant and stable now UNTIL I step on the brakes and clutch the same time quickly (like if you stopped for a deer in the road or something), that will kill the engine, every single time..no matter what.

Time to just bite the bullet and change all the upper gaskets (valve covers, upper & lower intakes) and hope it does the trick.

I've spent way too much time farting around with this thing, missing nice motorcycling weather (bought this truck as a cheap dirt bike hauler...yeah right!!)...and here in the Northwest, nice weather is a fleeting commodity!!

 

[Denisefwd93]

Brake booster???

OK,
With the new IAC, new TPS, and new throttle body I can get her down to a nice, steady 600-650ish RPM.

However, unhooking TPS at idle makes zero difference...cant get it to go any lower than 600ish even with screw 100% lifted off the stop of the new throttle body.

I also found when driving it, its much more pleasant and stable now UNTIL I step on the brakes and clutch the same time quickly (like if you stopped for a deer in the road or something), that will kill the engine, every single time..no matter what.

Time to just bite the bullet and change all the upper gaskets (valve covers, upper & lower intakes) and hope it does the trick.

I've spent way too much time farting around with this thing, missing nice motorcycling weather (bought this truck as a cheap dirt bike hauler...yeah right!!)...and here in the Northwest, nice weather is a fleeting commodity!!

 

[Vincenthdfan]

Brake booster???

I thought about that, but wouldn't it cause it to stutter at idle too??

I cant get any idle difference when sitting still and hitting or holding brake...

 

[Vincenthdfan]

Just outta curiosity, I went and bought a new vacuum gauge tonight (couldn't find my old one anywhere?!).

Installed vacuum gauge and engine held a steady 20 in Hg vac (using the power brake booster port on intake manifold) .

Blipped throttle, held throttle up higher, etc....always settled back to a pretty steady 20 in Hg vac.

Everything I read states that's indicative of a normal healthy engine and not a vacuum leak???

Ugh...

 

[RonD]

Good vacuum gauge tests here: http://www.gregsengine.com/using-a-vacuum-gauge.html

 

[Vincenthdfan]

Good vacuum gauge tests here: http://www.gregsengine.com/using-a-vacuum-gauge.html

Yep, that's the very page I used as a guideline...I have it saved in my favorites file.

So, now I'm even more confused as to why my truck will come to a nice steady stop without dying, but a quick stop will kill it every time?

Acts as though there is no dashpot function occurring?

 

[RonD]

If automatic shift to Neutral first then do panic stop, could be torque converter is not releasing quickly enough.

Jumper inertia switch temporarily, weight inside could be cutting power to fuel pump on sudden slowdown, without tripping it completely, never heard of that but free to try

"Dashpot"?
Thats carb technology, it prevented throttle plate from closing abruptly when driver took their foot off the gas pedal, what it did was to prevent sudden cut off of air to the engine, dashpot would hold throttle plate open, close to idle level, and then slowly close it from there to idle position, this lowered emissions, main purpose, but also prevented stalling.
Usually used on manual trans vehicles more than automatic, since automatics have the torque converter/fluid mass spinning so tend not to slow down fast enough to cause a stall or higher emissions

IAC Valve would be equivalent to carb's dashpot since it controls air flow into the intake when drivers foot is off the gas .

 

[Vincenthdfan]

:



I just got back from about a two hour long drive out through the country with my "new to me" Ranger.

That is the first time since I bought it that its left my immediate neighborhood and it drives like a dream now!!

No more fast idle, no more un-commanded low speed cruise control, and finally....no more stalling!!!

I re-installed the original Ford factory IAC which works far better than the new one I got from Auto Zone (twice!)....this took care of the racing fast cold start up caused by the Auto Zone one.

I have the newly re-conditioned throttle body that replaced the original which was badly grooved out by the butterfly on the throttle spring side of the throat...this took care of a consistently fast idle condition even when IAC was disconnected.

I replaced the TPS, which was causing the truck to have an un-commanded low speed cruise control when driving at low speeds....spooky stuff!

Finally, this morning I replaced the old cruddy looking fuel filter (of all things!) and this took care of the stalling every time I let off the throttle and hit the brakes. Funny, I've always been one to tell people that changing fuel filters rarely fixes problems, despite everyone always defaulting to them first because its easy, low hanging fruit....gotta eat crow on it this time because it fixed the stalling for sure!

It drove perfect all afternoon with not a hiccup or a single stall...just a nice, smooth, quiet idle and it pulled great at all speeds!!

Can you tell how happy I am now??

Now I can get onto other more esoteric tasks...I'd like to tighten my steering up a touch. It steers nice and straight in its lane, but its a little loose feeling in the wheel...despite the previous owner replacing most of the steering components. I believe the slop is in the steering box itself, I've read that's kind of a common trait of these rigs?

Probably replace the carrier bearing on the driveshaft, its a bit sloppy feeling too.

Oh yeah...the speedo is still off by several mph (too fast), despite changing the VSS and speedo head itself. I also verified the cable is nice and smooth. I suspect the drive gear is bad inside the transfer case. I want to install a manual transfer case anyway, so this gives me a good excuse to do so.


Other than that, just time to do some cosmetic touch ups....I have a whole new renewed enthusiasm for the rig now!!


Thank you for all the help RonD and Denisefwd93, you two were a very helpful (and patient!).

 

[Denisefwd93]

Congratulations!!! I don't know if Ford replacement parts are any better for this stuff

My truck has a very old sloppy carrier bearing.

It looks like I'm eventually replacing every component of the AC on my truck I'm heat intolerant so I have to have it to survive summer.

 

[RonD]

Yes, good work

 

[Denisefwd93]

Oh! Did you check the tire size on the door sticker for the original size tires? On my 93 I was shocked that it called for 265 75 R15, when I did get them, speedo was right on the money!