Chasing Idle/Temp issue after many parts replacements '93 4.0 ohv

[Eddo Rogue]

Hello all,
Long time reader, first time poster here. For the sake of attempted brevity, pardon my skipping formalities. But I will say thanks to all members for making this forum my ranger bible. After a decade plus of visiting, I finally joined.

Anyways, I have scoured every article to find a solution for my specific problem(s), and tried many suggestions and solutions, to no avail, which led me to join and post.

I have a beloved '93 Ranger extracab 4.0 ohv, 4wd, 5spd, 87k original miles! and here's a brief description of what led me to seek help...

A squeal under the hood and CEL led me to R&R the cam synchro (thanks to all the info found here). Along the way I also swapped the lower intake gaskets (leaked anyways), upper intake gaskets (why not), valve cover gaskets, pcv valve, replaced a few broken vacuum lines, replaced fuel injectors w/ new Bosch (they were caked in crud), and then gave the throttle body and intake a thorough cleaning (using a dremel and about a dozen brass wire wheels). everything past the throttle flap had heavy carbon buildup, which is why I also replaced the pcv valve.
After all this, she fired right up, no CEL, and runs like a champ! However I have 2 issues that still linger after throwing many parts and procedures at it.

1) High idle and hanging rpms.
2) Coolant temp gauge all over the place.

Problem 1:
Here's what I have thrown at the High idle issue:
-unplugging the IAC, the idle dropped slightly. I heard cleaning them can cause damage, so I replaced w/ a new aftermarket autozone unit. Didn't help.
-I put back the dirty original motocraft IAC, but now unplugging it did nothing, when previously it did slightly drop idle.
-taped shut the throttle body hole, it helped (went from 1500rpm down to 1000), adjusting the stop screw did nothing.
-drove around awhile for ECU to relearn, did nothing.
-sprayed and propaned around for vacuum leaks, nothing.

My next move(s):
-Ordered new Motorcraft IAC
-New IAT
-ordered stock used throttle body on ebay
- ordered Motorcraft pcv valve and hose to replace the aftermarket unit in it now.
-replace all the vacuum hoses.

Note: I recently replaced the DPFE and purge valve as well, and the truck passed CA emissions inspection last year, so Cats, 02's etc should be good...

Any other suggestions? maybe bad EGR? TPS? Internal vacuum leak?

Now for problem 2:
Here's what I threw at the temp fluctuation issue, which it does both at idle and under hard accel/load. ( Note: recently did waterpump and Explorer V8 radiator swap):

-replaced 180 thermostat with a motorcraft 195 unit ($30!!), then went back to the 180. Both fluctuate now.
-replaced both temp sensor/sender, wires looked fine. no teflon, so they should grounded
-inspected around my recently replaced waterpump, no leaks.
-bled/burped system on a steep hill (heater full blast, blows hot!), for about 40 mins until it stopped puking.... took about 6 gals coolant/distilled water.
My next move(s):
-try another factory temp thermostat. and another 180 thermostat (my truck seems to like the 180).
-give the motorcraft 195 thermostat I have now a chance to "break in".
-try a new heater core (the only thing I havent replaced).
-replace the upper hose maybe its collapsing?
-replace alternator (found a thread stating it could affect the temp gauge, and I wanted to upgrade to a 130 amp anyways)
-replace cap w motorcraft 16lb
-as a last resort I may replace the autozone waterpump w/ a motorcraft unit.

Just in case its related somehow, I did resurrect the A/C system along the way (thanks again to the tech articles here) and it works great now ice cold.

Any suggestions? faulty new thermostat? leakdown test? try again after the heater core swap?
Im getting tired of wasting coolant and gas burping the system after each parts swap....

BTW I just did the 1 piece driveshaft swap so finally solve my vibration problem (PITA!), and have an electric fan kit en route.

Thanks in Advance, my apologies for the long winded, disorganized error filled post lol, its been awhile since I've sat down and written anything (but do shorthand text chat alot!). I do plan to post some write ups w/ pics of my wrenching adventures, once I have reached the destination of my ranger being healthy again...and contribute back for all this place has given me.

Cheers! -Eddo




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[1986RangerXL]

I have a 2.9, but my high idle was caused by the TPS. I don't know exactly what you mean by hanging RPMs but the throttle can have hesitation when the TPS is bad.

Motorcraft and Hitachi? IACs seem to be the go-to but there are a couple cheap ones that seem to work okay.

And don't adjust that screw, big no-no here lol

 

[Eddo Rogue]

I have a 2.9, but my high idle was caused by the TPS. I don't know exactly what you mean by hanging RPMs but the throttle can have hesitation when the TPS is bad.

Motorcraft and Hitachi? IACs seem to be the go-to but there are a couple cheap ones that seem to work okay.

And don't adjust that screw, big no-no here lol

Thanks for the reply! Yea I'm thinking maybe my cleanout damaged the TPS, I will try this replacement used throttle body when it arrives...and if it works, replace the tps on my original unit, or go 66mm BBK

I mean when I hit the throttle, it doesn't just drop back down to "idle" like a normal engine, it hangs up a bit...

I have read the aftermarket are hit and miss, I think my replacement IAC was a duralast, I will try the new Motorcraft one that just arrived.

LOL yea I messed w/ the screw out of desperation :/, and hopefully set it back right, but will try the procedure I read of setting it just enough to keep the plate from sticking.

I think the revs dropping back down too slow and the high idle are related, will consider the TPS fix, thanks again!

 

[Dirtman]

I can only comment on a few things here.

1. never use a non motorcraft IAC valve. Before replacing it you should also just unbolt it and leave it plugged it. Turn the key to run and the valve should open about 3/8 - 1/2 an inch. And then turn the key off and it should close. If it doesn't move then the problem lies in the circuit, or the valve is physically jammed.

2. The stop screw on the throttle body should never be touched. It is not an idle screw, its for fine tuning the TPS sensor. Moving it screws up the TPS sensor. I would test your TPS sensor voltages now as it may be out of range, or it may have been broken from the start.

3. The IAC can be cleaned with anything, the throttle body cannot. Ford throttle bodies have a teflon coat on them. Cleaning them with a wire brush or carb cleaner will damage them and cause sticking throttle issues.

4. There is a coolant temp sensor and temp sender. The sender only controls the guage and has zero effect on engine performance. The sensor is the choke control for the computer. Sender is one wire, sensor is two wire. Did you replace one or both of these? Is the engine temp truly fluctuating wildy or is the guage just bouncing around? Its normal for the engine temp to rise and fall slightly as the thermostat opens and closes.

 

[Eddo Rogue]

I can only comment on a few things here.

1. never use a non motorcraft IAC valve. Before replacing it you should also just unbolt it and leave it plugged it. Turn the key to run and the valve should open about 3/8 - 1/2 an inch. And then turn the key off and it should close. If it doesn't move then the problem lies in the circuit, or the valve is physically jammed.

2. The stop screw on the throttle body should never be touched. It is not an idle screw, its for fine tuning the TPS sensor. Moving it screws up the TPS sensor. I would test your TPS sensor voltages now as it may be out of range, or it may have been broken from the start.

3. The IAC can be cleaned with anything, the throttle body cannot. Ford throttle bodies have a teflon coat on them. Cleaning them with a wire brush or carb cleaner will damage them and cause sticking throttle issues.

4. There is a coolant temp sensor and temp sender. The sender only controls the guage and has zero effect on engine performance. The sensor is the choke control for the computer. Sender is one wire, sensor is two wire. Did you replace one or both of these? Is the engine temp truly fluctuating wildy or is the guage just bouncing around? Its normal for the engine temp to rise and fall slightly as the thermostat opens and closes.

Thanks for the input!
1) Agreed, I have started to notice it is best to go motorcraft/oem in general. I am hoping the new motorcraft IAC will help, and will check in unbolted to make sure it works (will report back).

2) I did count my turns and feel I was able to get it back to original, because I don't notice my throttle sticking. I will test the TPS voltage, or just replace it...I will have to test voltage to adjust the new one anyways right?

3) Yea I may have been to heavy handed, probably will end up replacing both the throttle body and TPS...Rock auto has a decent deal about $80 after core exchange...Will report back on this as well. The new motorcraft IAC will go in as well. I may clean and keep the old one as a backup if it works after testing.

4)Yes I replaced both of them. The gauge will start moving up and down once I reach engine temp. it is intermittent but usually bounces around a bit during idle, and if I accelerate hard thru the gears, for example up an on ramp. The engine temp itself seems fine, though I may add a temporary aftermarket gauge to compare.

I read the thermostat will call a bit of fluctuation, but this Mine goes from middle to upper 2/3 back down to 1/3 and in between...never touches goes past the "L".

my old 180 thermostat kept just below the middle pretty steadily before I pulled it apart to do the cam synchro/intake.

I do suspect I am just not used to a motorcraft 195 ( always ran 180s), and maybe it needs "breaking in" to settle?

Thanks again, I will throw a meter on it and try your suggestions and report back

Im eager to get back on it, but of course its randomly pouring rain today in sunny Cali

 

[Dirtman]

On a fuel injection engine, always run the oem temp thermostat. There is zero advantage to a lower one. The engine and its cooling system were designed to operate at a specific temp. Sometimes a lower temp thermostat can actually make an engine run hotter because the coolant never has time to cool off properly since the thermostat is open too much. The computer knows that engine is going to be operating at say 205 degrees, this was engineered and the fuel trims are based on this number. On an old carbureted engine you could fiddle with this stuff. On an EFI engine, LEAVE IT ALONE!

Id get the new iac and throttle body on and go from there.

One of the problems with issues like this (in no way insulting you) is when you throw a bunch of new parts on without knowing if the old ones were bad. You now have new parts that you don't know if are bad either. Aftermarket electronic parts are a crapshoot so you could replace 5 things, fix one and have 4 new problems. Its called hitting it with the parts cannon, it rarely works out well.

 

[Eddo Rogue]

On a fuel injection engine, always run the oem temp thermostat. There is zero advantage to a lower one. The engine and its cooling system were designed to operate at a specific temp. Sometimes a lower temp thermostat can actually make an engine run hotter because the coolant never has time to cool off properly since the thermostat is open too much. The computer knows that engine is going to be operating at say 205 degrees, this was engineered and the fuel trims are based on this number. On an old carbureted engine you could fiddle with this stuff. On an EFI engine, LEAVE IT ALONE!

Id get the new iac and throttle body on and go from there.

One of the problems with issues like this (in no way insulting you) is when you throw a bunch of new parts on without knowing if the old ones were bad. You now have new parts that you don't know if are bad either. Aftermarket electronic parts are a crapshoot so you could replace 5 things, fix one and have 4 new problems.

I had to get over my cooler is better mentality, and realize the thermostat is the component that brings it up to temp, not cool it down. I bought a motorcraft 195 thermostat from rock auto and thats when it started to fluctuate. This is why I mention maybe it needs breaking in?

Also what are the chances I got a defective replacement 195 thermostat? I may buy another motorcraft or aftermarket premium thermostat to find out...

No offense taken, you are actually right. I am kicking myself in the ass now for doing it all once "while I had it apart", because now I am doing alot of it again trying to retrace my steps....and so far the common fixes aren't working. It is truly now a parts swap crapshoot, which I am hoping going motorcraft on everything this time around will help.

I never had these issues before, just the CEL bad cam synchro and intake coolant leak...at least those seem fine now lol

Thanks for the input!


Also I think the whole "replace this, and that goes bad" thing happened...like for example maybe when I pulled the intake something dislodged and clogged the heater core? far reach but idk

 

[RonD]

The heater core is the water pump by-pass on Rangers, so if the heater core gets clogged up the temp gauge will randomly go up above 1/2 and then back down, never overheat just temp gauge goes up and down for no good reason, lol

You can by-pass heater core to see if thats the problem, just connected hose together or use the longer hose to make the loop, from water pump to intake
Heater core is very easy to change on 1994 and earlier Rangers, just FYI, and not expensive


Maybe I missed it but to do the IAC Valve test engine needs to be FULLY warmed up

1993 Calif Ranger will have a high idle "hold" to reduce emissions
Idle should remain high between shifts and while speedometer is above 5MPH
Under 5MPH RPMs should start to drop to about 700 but other than that 1,000-1,100rpms is not unusual after warm up while moving

When refilling cooling system take off the intake side heater hose from the heater core at the firewall
That will let the air out of the engine when refilling, no burping needed, when coolant starts to come out of that hose put it back on the core, done and duner

Any air will be purged on the next heat up cool down cycle of this type of overflow/recovery system

Also reverse heater hoses at the firewall every year, this will reverse flow in the core and make it last longer, for ANY vehicle, you won't loose much coolant, just keep hoses high

 

[Eddo Rogue]

The heater core is the water pump by-pass on Rangers, so if the heater core gets clogged up the temp gauge will randomly go up above 1/2 and then back down, never overheat just temp gauge goes up and down for no good reason, lol

You can by-pass heater core to see if thats the problem, just connected hose together or use the longer hose to make the loop, from water pump to intake
Heater core is very easy to change on 1994 and earlier Rangers, just FYI, and not expensive


Maybe I missed it but to do the IAC Valve test engine needs to be FULLY warmed up

1993 Calif Ranger will have a high idle "hold" to reduce emissions
Idle should remain high between shifts and while speedometer is above 5MPH
Under 5MPH RPMs should start to drop to about 700 but other than that 1,000-1,100rpms is not unusual after warm up while moving

Yes I heard the same thing, internal bypass...and they are easy on these trucks (I had same truck diff color in college, and wrenched on it alot). I ordered one.
the motorcraft unit was $130, but I heard good things about the spectra premium, and went with that one for $20....should arrive by tomorrow.

Good call in the IAC test, I will perform it warm.
I knew there was something funky emissions related to the idle, thanks for clarifying that (makes sense too).

Right now its at 1500 steady hot or cold or above 5mph, and sometimes drops to 1k steady (especially since I taped the throttle plate hole shut)

I read a post about a member who tried the tape trick, which worked so he soldered the hole shut and drilled in a smaller one to fix his idle...

I may bypass the core to test it unless the new one shows up soon...planning a desert run test drive this weekend, been doing way to much wrenching and too little driving lately.

will update my results after the next wrench session

 

[RonD]

To set anti-diesel screw(looks like idle screw, lol) you warm up the engine fully
Unplug the IAC Valve's 2 wires
Back the anti-diesel screw out until RPMs are 500-600 or so, barely running, its SET

Now if the RPMs do not drop then something is holding throttle plate open or there is a vacuum leak
A 3rd part TPS can hold open throttle plate, as can throttle cable or cruise cable
Take off TPS and cables, retest

The tape over the small hole in throttle plate is OK but not solving the problem, lol
If the throttle plate bushings are leaking then it can be used instead of new throttle body

Try taking off power booster vacuum hose and PCV hose first and plugging ports

Don't try to overthink things, KISS is the key to these systems

 

[Eddo Rogue]

To set anti-diesel screw(looks like idle screw, lol) you warm up the engine fully
Unplug the IAC Valve's 2 wires
Back the anti-diesel screw out until RPMs are 500-600 or so, barely running, its SET

Now if the RPMs do not drop then something is holding throttle plate open or there is a vacuum leak
A 3rd part TPS can hold open throttle plate, as can throttle cable or cruise cable
Take off TPS and cables, retest

The tape over the small hole in throttle plate is OK but not solving the problem, lol
If the throttle plate bushings are leaking then it can be used instead of new throttle body

Try taking off power booster vacuum hose and PCV hose first and plugging ports

Don't try to overthink things, KISS is the key to these systems

Awesome thank you, excellent suggestions. Definitely trying to KISS it from here on lol....

Ok I am gonna start by throwing the motorcraft 195 thermostat back in, and put everything back in so I can run it and do these tests...Just about every reply has supplied a good suggestion or test to try, which has me eager to throw it back together and running start testing.

I am gonna test and install my new motocraft IAC
Then replace IAT sensor, which looked like crap when I had the intake apart
Then hit the throttle body, which suspect is the problem...I think my wire wheel job messed it up. I will do the screw set procedure u suggested, and perform the tests for shits and giggles, but if anything comes up I will replace the whole unit, no messing around. Maybe even replace it w/ a BBK 66mm, again for shits and giggles, and in case I do modify the motor to make use of it later.

I plan to keep this truck forever, and dont mind throwing relatively little money at it (it aint a bmw). I also just have a weird attachment and fondness for Rangers, and enjoy spoiling on mine...I dont care about hp or gas mileage, I just want a properly running happy and relatively bulletproof motor (and drivetrain for that matter).

Now Im developing a gut instinct its definitely something w/ the throttle body. Gonna reassemble to the stage of focusing on that

Afterwards Im thinking bypass the heater as my next test for the temp issue....

I forgot to mention before all this, back before even the cam synchro went bad, I had a temp gauge issue, which swapping the sender fixed. so basically I replaced the new Sender and the old sensor this time around....

Im building quite a stack of "backup spare" parts lol

I also just got a brand new intake tube to replace my beat up old one...it was spendy but sexy, and hopefully it helps.

This is all much appreciated, keep em coming!

 

[Eddo Rogue]

To set anti-diesel screw(looks like idle screw, lol) you warm up the engine fully
Unplug the IAC Valve's 2 wires
Back the anti-diesel screw out until RPMs are 500-600 or so, barely running, its SET

Now if the RPMs do not drop then something is holding throttle plate open or there is a vacuum leak
A 3rd part TPS can hold open throttle plate, as can throttle cable or cruise cable
Take off TPS and cables, retest

The tape over the small hole in throttle plate is OK but not solving the problem, lol
If the throttle plate bushings are leaking then it can be used instead of new throttle body

Try taking off power booster vacuum hose and PCV hose first and plugging ports

Don't try to overthink things, KISS is the key to these systems

Forgot to mention I wanna wait until my new motocraft pvc arrives for that...I have a shitty aftermarket one right now I am suspect of...

I will try the power brake hose test...

and yes I don't intend to stick w/ the tape on the throttle plate, pun slightly intended lol

 

[Eddo Rogue]

The heater core is the water pump by-pass on Rangers, so if the heater core gets clogged up the temp gauge will randomly go up above 1/2 and then back down, never overheat just temp gauge goes up and down for no good reason, lol

You can by-pass heater core to see if thats the problem, just connected hose together or use the longer hose to make the loop, from water pump to intake
Heater core is very easy to change on 1994 and earlier Rangers, just FYI, and not expensive


Maybe I missed it but to do the IAC Valve test engine needs to be FULLY warmed up

1993 Calif Ranger will have a high idle "hold" to reduce emissions
Idle should remain high between shifts and while speedometer is above 5MPH
Under 5MPH RPMs should start to drop to about 700 but other than that 1,000-1,100rpms is not unusual after warm up while moving

When refilling cooling system take off the intake side heater hose from the heater core at the firewall
That will let the air out of the engine when refilling, no burping needed, when coolant starts to come out of that hose put it back on the core, done and duner

Any air will be purged on the next heat up cool down cycle of this type of overflow/recovery system

Also reverse heater hoses at the firewall every year, this will reverse flow in the core and make it last longer, for ANY vehicle, you won't loose much coolant, just keep hoses high

awesome I knew there was a trick to bleeding...Um which side is the intake? Im thinking it would be the hose coming off the waterpump, correct? I wanna try this, burping it sucks!

 

[Eddo Rogue]

OK so I went for a test drive...I think I fixed the idle issue...was at about 1250rpm cold, then settled down to purring at about 750rpm. I think it was the IAC, both my old original ford, and aftermarket autozone replacement were no good, and the new motorcraft unit did the trick.

I still have tape over the throttle plate hole...Might just remove it and go from there...

temp gauge is still dancing back and forth between O and L...wont stay put longer than 1 minute. gonna bypass the heater core and try that.

Also I threw a CEL, but I think its because I forgot to connect the oil breather hose, which may have caused my egr vacuum lines to blow off? (they were disconnected at the egr tube when I pulled in)...gonna clear codes, reconnect lines, pull tape off throttle plate hole, and do another hot lap...

I dont get it, his thing runs like a beast! I cant wait until these bugs are gone...

On the plus side, my 1 piece driveshaft swap worked like a charm! never had such smooth and vibration free ride, even felt like the power was hooking up better, with less slack in the transfer from engine to wheels. Made the truck feel "lighter".

 

[RonD]

On 4.0l OHV engine, just above thermostat housing on the intake manifold is a heater hose, thats the high point of engine cooling system, so as you refill via radiator air will flow out of that hose until engine/heads are full, no air