93 Ranger 4x4 4.0 High Idle / Drivability Problems

Hello all...first post is gonna be a doozie, but here goes!!

I have a "new to me" 93 Ranger 4x4 that I bought with a leaking and slipping A4LD transmission in it.

I decided after researching the trouble prone nature of those trannies to convert the truck to a 5 speed.

I swapped everything over (to include the ECM computer from auto to standard 4x4 model), got everything done and noticed truck seemed to idle pretty high, even after being warmed up.

Side note: To be totally honest, I believe this engine run-ability/drivability issue was there before I swapped it over because it died when doing sudden stops on the way home with it too. But...it was leaking so badly, I never really got the opportunity to get to know the truck before tearing into it because it was leaking tranny fluid and slipping so badly.

On initial start, with original FOMOCO IAC still installed, it started up at 1800 rpm, dropping down to 1000'ish when warm.

I unhooked IAC wires, no change...

Installed a new IAC...whoa! Revved to 2500 rpm cold start, settled down to 1000'ish when warm.

Cleaned MAF with MAF cleaner.

Checked throttle stop screw and it was set correctly.

Carefully sprayed carb cleaner around vacuum lines, PCV Valve & hose, intake joints....no change.

With old IAC installed I can live with the idle and drivability except for when driving along on flat ground.

It acts like cruise control is set at any speed above 15 MPH. It will literally stay at 1800 RPM's at anything above 15 MPH on flat ground, foot off accelerator it just putts along on its own.

With the new IAC installed, its even worse...hauls butt above 15 MPH because idle wont settle below 2300 RPM's even with foot off pedal.

You literally have to drag the brake to slow down on level ground.

I'm at a loss here and could really use some advice if there's any out there to be had?

I've search functioned this to death, but this situation seems unique.

Oh, another thing its doing and has been since I attempted to drive it home....may, or may not be related...the speedometer is consistently reading about 10 to 15 MPH high as checked against my GPS.

I thought maybe the VSS was causing an issue with computer when driving, so I swapped it out with one from the 5 speed donor truck, still no difference there?

I'm a retired aircraft mechanic that knows my way around a wrench and a multi meter, so I can troubleshoot if pointed in the correct direction.

RonD....I sure could use your help buddy!!

I have the same truck same problems
When you went to manual you probably have a transmission and speedometer gear issue. You may want to check the door sticker for the tire size.

I just picked up a 94 we put a transmission. and I've been futzing on it for weeks. it had a fast idle. changed the IAC x2 also changed the TPS x2 and cleaned the MAF. Starts with high RPM and drops right down to about 1,200 then warms up and drops down to about 600 - 700.

Sounds like it's vacuum to me. Have you disconnected and plugged the brake booster as a check on the diaphragm?

Denisefwd93 said:

I have the same truck same problems
When you went to manual you probably have a transmission and speedometer gear issue. You may want to check the door sticker for the tire size.

I just picked up a 94 we put a transmission. and I've been futzing on it for weeks. it had a fast idle. changed the IAC x2 also changed the TPS x2 and cleaned the MAF. Starts with high RPM and drops right down to about 1,200 then warms up and drops down to about 600 - 700.

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Yeah, I have been reading your posts regarding your swap.

It was actually quite fun doing it on this truck and I'm hoping it'll be worth it in the long run...mainly because its the perfect (and hard to find!) combo.

Great, long lasting engine and a long lasting transmission with 4x4, cant beat that combo!

I'm curious how yours ended up dropping down, because mine sure wont go below 1,000 no matter what I try.

I haven't messed with the TPS...yet.

Perhaps that's something to pursue as well.

alwaysFlOoReD said:

Sounds like it's vacuum to me. Have you disconnected and plugged the brake booster as a check on the diaphragm?

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That thought crossed my mind too...

Its gotta be a vacuum issue somewhere??!!

After engine is warmed up shut it off and remove gas pedal and cruise cables from throttle linkage

Restart
See what idle is at now(maybe someone got carried away on throttle cable mod, lol).
See if you can close the throttle more, manually, could be spring is weak and can't hold throttle plate closed all the way
Incorrectly installed TPS can hold throttle open a bit

On the throttler linkage is an "anti-diesel screw" looks like an idle screw but isn't because we all know fuel injection can't use an "idle screw",
Unplug IAC valve wires, leave engine running
Turn the screw counter clockwise, see if idle goes down

If it does then keep turning it until idle is at about 500rpm, under 600 for sure
Plug IAC Valve back in and RPMs should go up to about 650

If idle doesn't drop then put screw back where it was

Leave IAC Valve unplugged
Now unplug each vacuum hose on the intake, one at a time, start with power brake booster and PCV hoses, cover the open port with your finger to see if RPMs drop.
Repeat for all hoses on intake.
If RPMs drop you found the system with the leak

A bad PCV Valve can be a vacuum leak, testing its hose will show that

Lower intake on the 4.0l OHV engines got leaks often, the bolts would loosen up, check that gasket with a spray bottle of soapy water, better than flammable fluids on warm engine, engine will stumbled if it sucks in soapy water.
If you ever change a lower intake gasket on a 4.0l always use locktite on the bolts or they WILL back out

Also spray fuel rail upper intake gasket areas

RonD said:

After engine is warmed up shut it off and remove gas pedal and cruise cables from throttle linkage

Restart
See what idle is at now(maybe someone got carried away on throttle cable mod, lol).

On the throttler linkage is an "anti-diesel screw" looks like an idle screw but isn't because we all know fuel injection can't use an "idle screw",
Unplug IAC valve wires, leave engine running
Turn the screw counter clockwise, see if idle goes down

If it does then keep turning it until idle is at about 500rpm, under 600 for sure
Plug IAC Valve back in and RPMs should go up to about 650

If idle doesn't drop then put screw back where it was

Now unplug each vacuum hose on the intake, one at a time, start with power brake booster and PCV hoses, cover the open port with your finger to see if RPMs drop.
Repeat for all hoses on intake.

A bad PCV Valve can be a vacuum leak, testing its hose will show that

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Yeah, I did the anti-diesel screw...it dropped maybe 50-75 RPM (if even that much) unfortunately, so I just put it back where I found it.

I have pulled and plugged several vacuum lines and PCV line...no difference, haven't done power brake hose yet though.

I noticed that you wrote this in one of your posts regarding the MAF sensor:

MAF sensor can be left unplugged

You will just get a code that it is not working, if you have driven it without MAF connected

Codes mean computer is working, you can "talk" to it, or rather it can "talk" to you by outputting codes.
If the computer gives you, no codes or "oddball" codes, or multiple codes for "working" systems then computer is the problem.

I remember the other day when I unplugged MAF when engine was running, the idle dropped on its face and motor ran rough...is that normal, or is that my issue maybe??

RonD said:

Lower intake on the 4.0l OHV engines got leaks often, the bolts would loosen up, check that gasket with a spray bottle of soapy water, better than flammable fluids on warm engine, engine will stumbled if it sucks in soapy water.
If you ever change a lower intake gasket on a 4.0l always use locktite on the bolts or they WILL back out

Also spray fuel rail upper intake gasket areas

Click to expand...

I sprayed those areas with Carb Cleaner today, albeit very gingerly, as I had visions of fireballs on my mind, lol. I got no RPM change results though...I suppose I'll try water tomorrow, a little less sparingly.

I intend to do valve cover gaskets on it soon, they've never been done and it has 152,000 miles on it so they're leaking pretty good. Maybe I should bite the bullet and do lower intake too at the same time....just hate to do it and it produce no results?

The MAF can't cause a high idle, it could cause poor air/fuel mix.
Try unplugging MAF first then starting engine

Computer is programmed for a 4 LITER engine, so it already knows how much air will be coming in at any given RPM, its just math and thats all the computer is really setup to do, fast large number calculations, air/fuel ratios on the fly

MAF sensors main function is air temp and air density(altitude), in 1993 there is a separate air temp sensor(IAT) but MAF is still part of air temp.
MAF sensor part gets 5volts and sends back .3 to 3.5v
.3 at idle. 3.5 at wide open
When you unplugged it, voltage drop may have caused computer to goof up on the mix
So try unplugging it first, so computer "knows" there will be no MAF data coming so it will use standard mix tables.
And it really depends on software used, there were multiple software versions in every year.

Higher idle has to be too much air
If you add more fuel to an engine you get a Flooded engine, not higher RPMs, well maybe a few seconds of higher rpm, not continuous.
If you add more air you get higher RPMs, point of the throttle plate and the "air" pedal to open it

I would read the codes, just need a short jumper wire to do that
Video here: https://www.youtube.com/watch?v=X07hu0kAuzE
1993 will be 3 digit codes, seen here: http://www.therangerstation.com/how-to/ignition-charging-computers/obd-i-diagnostic-trouble-code-dtc-applications-ford-3-digit-codes/

You should have a MAF code

Sounds more and more like a lower intake gasket I'm thinking??

Pretty common leak point you say...especially after 152,000 miles?

So, I've been spraying copious amounts of Carb Cleaner around my hoses, fittings, joints, etc. all to no avail.

I did it motor hot, motor cold, IAC connected, IAC disconnected...no vacuum leaks detected.

I did find the airbox end of my intake tube weather checked pretty bad on the bottom, right near the MAF sensor. I taped it all up and it made zero difference.


I got looking at throttle body butterfly and thought, wonder what it'll do if I block that bleed hole in the throttle plate?

I taped it up with some heavy duty tape and whoala...it idled right down to 500 rpm with IAC disconnected and idled at 650 RPM with IAC connected!


I know that isn't really a fix, but just masking the problem by effecting air intake ratio.

My question is though...do throttle bodies wear around the perimeter of the throttle blade over a period of time?

Could that be enough to be causing this high idle issue I am experiencing?

Or is that wishful thinking?

Hate to go out and buy a throttle body and have zero change...they aren't cheap.

I don't think it's possible for a throttle body to wear out.

Just a suggestion, do you have the old computer for the automatic? I mentioned this on another post about the same topic.

Denisefwd93 said:

I don't think it's possible for a throttle body to wear out.

Just a suggestion, do you have the old computer for the automatic? I mentioned this on another post about the same topic.

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I do have the original automatic computer (not installed of course).

I've read that they will rev high because they're looking for transmission solenoids that are no longer there.

I just got back from a test drive with that bleed hole taped over and it drove great...just like a normal truck would (or should).

Frustration continues...

Vincenthdfan said:

I do have the original automatic computer.

I've read that they will rev high because they're looking for transmission solenoids that are no longer there.

I just got back from a test drive with that bleed hole taped over and it drove great...just like a normal truck would (or should).

Frustration continues...

Click to expand...

Where is this bleed you're referring to, you have a picture?

Denisefwd93 said:

Where is this bleed you're referring to, you have a picture?

Click to expand...

Inside the throttle body, on the actual throttle butterfly valve/plate it self.

There is a factory hole drilled right below the pivot shaft.

My theory was, if I have a massive vacuum leak providing air elsewhere, the hole covering should make little difference...but, I may be incorrect in my thinking altogether?

It did however, make it act like a normal rig would.