Hello

My brother got a 1999 ford ranger 4.0 4x4 manual about a year ago. It was idling higher than it should at around 1100-1600 rpm, no check engine light but was running rich and seemed to burn more gas than it should. Around December we cleaned the throttle body, cleaned the mass air flow sensor, intake air temperature sensor and replaced the fuel filter along with an oil change. After this the truck had more power (probably a result of the clean fuel filter). However, after this the truck started idling at around 2000 rpm! We then discovered the truck's check engine light was burned out (not a good sign). The truck had the following codes.

P1506 - idle air control over speed error
P0136 - O2 sensor circuit bank 1 sensor 2
P0141- O2 sensor circuit bank 1 sensor 2
P1132- Lack of HO2S11 Switch/ Sensor indicates rich
P1152- Lack of HO2S11 Switch/ Sensor indicates rich

We then noticed that the truck has had the catalytic converter removed and a dummy O2 sensor added. We replaced the idle air control valve for the old one was is bad shape. When just the dummy sensor is unplugged the truck idled at about 1600 rpm but was smoking a little. We then unplugged the idle air control valve with the dummy sensor unplugged it started up idling at 6-700 rpm then the idle crept up to 1200 but the smoke stopped.

I also have a theory that the throttle body seal was wrecked when we cleaned the throttle body. We tried covering the two holes on the throttle plate to make the air getting past the throttle plate more similar to if there was not a leak. We tried this with the idle air control valve plugged in and with the holes covered up the idle was 200 rpm lower than with them open. When the idle air control valve was unplugged with the throttle plate holes covered up the truck idled at 1100 rpm but the truck was smoking again.

I don't know if this is a separate problem but we knew the truck burned a little oil but when I checked it it was black like diesel oil but it has been less than 2000 miles since the oil change. This is with synthetic oil that is still somewhat golden when it is time for oil changes in our other vehicles.
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Lastly we have tried checking for vacuum leaks by spraying carburetor cleaner around the intake and vacuum lines and have not been able to find a leak.


What can we do to make the truck run and idle properly or as properly as we can? Is it necessary to source a catalytic converter and put back into the truck and hook up a good oxygen sensor? Does my theory about the throttle body seal being damaged sound right? Should we replace the throttle body?

Any tips are appreciated and thank you all in advance for your help.

 

46 reads but no replies yet, so I'll see if I can get things started. Good idea to have scanned for & posted the trouble code clue Numbers, as they can help focus a trouble shoot.

SO, lets think about this some more. Seeing as how the CEL was burned out, the cat converter removed, the O2 sensors not switching (stuck at Rich), its not yet clear if its over rich because of a over fueling condition caused by something like too much fuel pressure, or dirty fuel injectors with a runny nose, wrong injectors installed by someone trying to make more power & not knowing what they were doing, or...., well you get the idea, we need some more testing clues, to help focus where best to look next!!!
So use your fuel pressure gauge to perform a fuel pressure & pressure bleed down test, to get an idea whats going on with the fuel delivery side. Fuel pressure should be 64 +/-8 psi & psi should hold for 1/2 hour or so, without significant drop off from leaky fuel injectors, or a faulty / leaking fuel pump psi relief / anti- drain back valve.

IMO I'd install the proper cat converter, so our factory tuned system is scavenging exhaust as designed.

Was a plastic safe, non residual, cleaner, like CRC MAF Sensor spray, used to clean up the MAF sensor?

Some initial thoughts for consideration, let us know how it goes.

 

Thank you for the response

The cleaner used was a dedicated MAF cleaner, I believe it was CRC

We will be borrowing a fuel pressure tester and testing it on the weekend. We did some more testing and found it quite evident that with the idle air control valve plugged in the PCM tried to make it idle up every time to about 2000 rpm. With it un plugged it did not return to a normal idle but was lower (about 1000 rpm). This was all done on a cold engine. We also read on my scanner that the truck was trying to lean out the mixture but was not able to (I cannot remember the value)

What sensors are providing feed back to the PCM when the engine is cold that would command it to idle up? We were told by a mechanic that it should run mostly be off set values in the computer until it warms up. The next question is what could cause the idle to be above factory spec with the IAC valve un plugged not allowing an air by pass. Does this indicate that the throttle plate idle screw was tampered with? Again we will be testing the fuel pressure to see if that is the problem but I am trying to understand how this system works more. Thanks

 

Ok good feedback & to hear the MAF sensor was cleaned with a dedicated non residual cleaner, so to not leave drying residuals on the heated MAF sensor heated wire, or the IAT sensor, thats located in this assembly, as, residuals could corrupt its PID feedback to the ECM & further complicate the troubleshoot.

If fuel pressure & pressure leak down check out ok, with the O2 sensors not switching / stuck rich, it would suggest a bad vacuum leak,that the ECM is trying to correct for, so have a look at all vacuum lines & vacuum controlled / operated things & this would also include the in cabin vacuum operated Heating / AC controls, upper & lower intake manifold gaskets & the PCV valve & All its rubber plumbing parts. The pcv valve rubber elbow likes to crack, unseen on its Outer radius so be sure to inspect All closely. as this vacuum leak is downstream of, so not measured by the MAF sensor, so it leaking can really corrupt fuel trim & idle speed so much that the IAC, O2 sensors & fuel injectors may not be able to compensate. SO, if it is a gross vacuum leak, it should be fairly easy to locate without having to rig a smoke test to find a bad vacuum leak.
More thoughts for consideration, let us know what you find.

 

My 94 3.0 idled very high, almost 2000 rpm’s sometimes, ran rich enough that you could smell gas from the exhaust pipe, and it smoked a little.
I changed the temperature sending unit that the computer reads, and that took care of it. If I remember correctly, there are 2 sending units- one that runs the gauge and one for the computer.

 

Sorry for the long time away. My brother has been off at school and left the truck in our shop. While he was back at Christmas we looked over things. We did a fuel pressure test and bleed down test and everything was within spec. We cannot find any vacuum leaks and the ac vents have been working as they should.

I just saw pram703 post about the temperature sending unit. We will look into that soon.

Other than that we cannot think of other sensor inputs that would cause the truck to run so rich. We were wondering about the oxygen sensors but our cousin who is a retired Ford mechanic said that the computer does not even look at those until the engine is warmed up. When he was over I had my reader on the truck and I remember him saying the truck was trying to run less rich, I do not know which parameter he was looking at.

If the temperature sensor is not the problem is it reasonable to think that the ECM is bad. Can a truck this old be re flashed at a ford dealer or are we stuck looking in wrecking yards for one. Our cousin said in his experience the ECM rarely is the real problem but we are running out of ideas.

 

I agree with the vehicle computer / ECM not likely the root cause of the fuel trim problem, ( Banks 1 & 2 O2 / sensors not switching, stuck Rich). so lets think about this some more.
On the Vacuum leak feedback, you didn't mention having checked the PCV system rubber parts, or the PCV valve itself, nor the 4 X4 pvh system. Both of these Vacuum systems are downstream of & thus arent monitored by the MAF sensor & both have rubber components with known tendencies to develop vacuum leak problems that'll corrupt fuel trim, so be sure to give them a thorough vacuum test & vacuum parts a visual inspection.
With the cat converter gone, & the after cat O2 sensor reading been messed with, sounds like this problem has been around for a while, so no telling how long the engine & oil has been put upon in having to deal with extra soot load & fuel dilution!!!

 

We looked into the coolant temperature sensors. We had left the heat off in our shop for a few days so it was -1.6°C (29F) air temperature measured around the truck. We plugged in my scanner and read the coolant temperature which read 6°C (43F) and rising with the truck on. I would assume that the input read on the OBDII scanner is the same one read by the computer so this does not seem to be the problem. I just happened to look at the intake air temperature sensor which I read can also cause a rich condition and it read -5°C (23F) which is colder than the air temperature we measured. Is this suspicious or is a 3.4°C difference expected.

As for the vacuum leaks we have checked thoroughly. The PCV valve rattles when shaken and the hose is still soft. The 4x4 hubs engage as they should and we have looked over the lines. When our retired Ford mechanic cousin came over he could not hear a vacuum leak and mentioned if it was too big of a vacuum leak it would just stall and showed us by removing the brake boaster hose and the truck stalled. Could a vacuum leak cause the engine to idle 1000-1200 rpm higher than it should without stalling the truck? We have sprayed carb cleaner around the engine and listened carefully for vacuum leaks but have not found any. Should we try a smoke machine? It feels unlikely that it is a vacuum leak after all our looking.

We are leaning towards a fuel issue rather than an air as the idle got worse after changing the fuel filter.

The other thing we have noticed is even if we let the truck sit for a weak with the battery disconnected then connect it and start it 5 seconds later it immediately idles at 2000 rpm.

Could it be a bad tune someone put on the truck? is there a way to check this?

 

A PCV Valve shake / rattle test isn't valid, as it just says it isn't mucked up solid, it doesn't test for poor worn seating, or worn out / wimpy spring. If its time, worn, or otherwise suspect, replace this inexpensive scheduled maintenance item. You didn't mention if the PCV rubber elbow OD was inspected for cracks / splits, as it likes to crack on the Outsede of the elbow bend & is a common vacuum leak suspect area.

With the O2 sensors not switching / Stuck Rich, have the scan tool look at fuel injector squirt time to see if its long or short. If long, the computer is trying to correct for a vacuum leak. If its short, its trying to correct for too much fuel, like dirty, or worn-out runny nose injectors, or maybe high fuel pressure, or maybe the wrong fuel injectors have been mistakenly installed, or maybe someone was trying to make more power but lost their way???

 

Thank you pawpaw we will try to look at that this weekend

 

We've spent 1500. trying to figure this out, parts and labor! Still has the same issue acts like it's on cruise control and will keep the existing speed up without using the gas pedal. Changed ERG, sensors galore and still can't find the issue. Idles high, so it was lowered and still does this same thing...... Any ideas? Ford dealerships had it twice and can't figure it out. Thinking of selling it but it only has 115,000 miles everything else tests out good no engine light.

 

Welcome to FTE.
No replies yet so will see if I can get things started.
You've revived a 2+ year old open thread that the OP has yet to close, so we don't yet know if his high idle problem trouble shoot was put right or not.

I'd suggest starting a new thread by going here 1983 - 2012 Ranger & B-Series - Ford Truck Enthusiasts Forums (ford-trucks.com) & clicking on the + new thread button atop the left side of the forum header thread page stack, so you get answers just for your problem.

You've done lots of work but there are still lots of unknowns to the forum.
Did the problem come about slowly over time, or suddenly after some event???
Were all those replaced parts testing bad, or were they replaced on a hunch???
Did you have trouble codes stored, if so, post All code Numbers as they can help focus a trouble shoot.
Does the CEL light up for its self-check at key on???

Some beginning thoughts for consideration you can answer in your new thread, hope to see you there.

 

***change idle air control valve

 

Over due update.

We have changed the fuel injectors with good used ones and the truck runs perfectly with the idle air control unplugged. The injectors helped a fair bit. As soon as the IAC is plugged in it will idle high again. My brother has been driving it all winter like this and getting mileage that is normal for a 4.0 ranger. The truck is burning a little oil so it seems like my brother is not going to address the remaining idle issues on this motor.

 

If it's any consolation, we've had ours in the Ford shop locally and are at 1200. trying to fix this problem. At this point we are taking it back again today to see if they can fix it...Otherwise we'll sell it. What a pity! Even Ford can't fix it. The truck is like it's on cruise control and has power surges, any ideas!!!