2002 Ranger 4.0 idle

Hello everyone! Just recently found this forum, I've been watching the youtube videos recently. Great youtube channel!

I have a 2002 Ranger 4.0 auto, that I bought back in August. When I bought it, it was a no-start vehicle. That turned out to be just the clutch bypass had been removed by a malicious person the previous owner knew (and that person is actually now incarcerated for other reasons).

First thing I did was to get that wired up, and the truck started right up. Ran decently, but without knowing the history on the vehicle, I went after all the normal things I replace: plugs, wires, oil change, trans fluid, etc. I didn't really drive it much before I did this work, so I don't recall exactly if it had this idle issue at first or not. Finally start driving it, and it drives well, but has a misfire at idle, no codes.

Then it starts to have a fuel pressure leak down issue, which was either the pressure regulator or the pump, but they are both on the assembly in the tank. So that got replaced, and it holds fuel pressure while off again.

Back to the idle; still feels like it misfires, particularly when in gear at a stoplight. The truck with often stumble quickly, pick up the throttle, then go back to normal. So I feel the whole truck jump a touch. Took the plugs out, inspected, made sure I seating them all correctly. Verified wires were good. Tested coil pack. Found ScannerDanner videos, started watching those. Watched my fuel trims, O2 sensor readings, TPS, IAC, etc. During this process, I noticed the knock sensor wires were exposed, and the only way to replace the knock sensor is to remove the intake manifold (plastic, with O rings to seal). Ordered a new knock sensor, replaced O rings on manifold. The misfire count doesn't jump up anymore like it was doing (when I noticed the wires, they were actually touching each other). But it still stumbles/misfires at idle. As soon as I get off idle, it feels great.

Watched another video today, then went out and got some readings. I watched the IAC position, TPS voltage, RPM, desired RPM. The computer wasn't able to get the RPM to match the desired RPM. It commanded around 700, but the idle was sitting up around 800-900, with the IAC down around 21-22%. TPS voltage was at 0.95V. LTFT at idle is typically -9 to -12, both banks.

From what I've read, and watched, it seems like it could be a vacuum leak. But I cannot find the culprit. Very open to suggestions. (inspecting the throttle plate screw, it doesn't appear that it's been adjusted before)

Hi Speedwagon,
Typically, when you have a vacuum leak, the fuel trims are usually reading + and also usually above 15-20% at idle (or above if a bad one). When the idle rpm is raised to 2000 or above, the fuel trims will come back down to the normal single digit range. Since your IAC percentage is 21-22%, you may have a faulty IAC. Try disconnecting it and see what happens. The engine may stall or still continue to idle but at a pretty low speed. Do you have access to a smoke machine if need be?
Thanks,
Doug S.

DougS wrote: Hi Speedwagon,
Typically, when you have a vacuum leak, the fuel trims are usually reading + and also usually above 15-20% at idle (or above if a bad one). When the idle rpm is raised to 2000 or above, the fuel trims will come back down to the normal single digit range. Since your IAC percentage is 21-22%, you may have a faulty IAC. Try disconnecting it and see what happens. The engine may stall or still continue to idle but at a pretty low speed. Do you have access to a smoke machine if need be?
Thanks,
Doug S.

I did disconnect the IAC, and the RPM did drop a little, but not by much. As soon as I plugged it back in, the RPM kicked up briefly, then lowered again. But still above the commanded RPM.

I made a DIY smoke machine, but haven't had luck finding anything yet.

Speedwagon,
Did you note your fuel trims at idle and again at 2000 RPM or so? What were they and were they reading Positive or Negative?
Thanks,
DougS

DougS wrote: Speedwagon,
Did you note your fuel trims at idle and again at 2000 RPM or so? What were they and were they reading Positive or Negative?
Thanks,
DougS

At idle, I recall them being around -9 to -12. At higher RPMs, they go down closer to 0. If memory serves, -2 to -5. But the below screenshot shows different numbers. Possibly I am remembering numbers from the vehicle at different conditions.

Edited: It seems the IAC is fully closed when the vehicle is fully warmed up, since it did not change the RPM when I disconnected it. The following post shows that it is functioning when cold.

2 screenshots: plugged in, then unplugged IAC.

Tested the IAC again this morning, with a dead cold engine. It is certainly working. Engine almost died when I unplugged it.

I would check pcv valve. One way to tell is pull oil fill cap off does it die when you take it off.

Hardtopdr2 wrote: I would check pcv valve. One way to tell is pull oil fill cap off does it die when you take it off.

That was one of my early thoughts, so I replaced it given the mileage of the vehicle (185k).

But I think I may have found the culprit. When I replaced the intake manifold o rings, I noted a good location to hook up my DIY smoke machine to, that I had previously not seen because it was a bit buried. So I traced that line, and hooked up to it just now. Nothing coming out.

So I then hooked my vacuum gauge up to the vacuum hose I pulled off, and couldn't hold vacuum. It goes to the evap canister purge valve. I had previously tested that, by pinching off the purge line, but didn't think to test the vacuum diaphragm itself. Pulled the valve, and hooked directly to the valve, it holds no vacuum.

Edit: Well, nope. That can't be it. No change when I plugged that vacuum line, and disconnected the IAC at idle. Still doesn't drop the engine down when hot. And I have an 02 Explorer in the garage waiting on a fuel pump, same purge valve. Same result. I don't understand quite how this valve works, but neither of them hold a vacuum on the vacuum port.

You may need to bidirectionally control the valve closed with a scanner. Plug the hoses to the purge valve and see if short term trims go to zero/improve.

Also with the iac if you disconnect the battery cables (both positive and negative ) and hold those together for 2 minutes that should clear the memory for iac control. Then reattach it should return to matching commanded rpm. (It worked for me on a mazda 3.0 (fords 3.0). Let me know

Be sure to carefully inspect both top and bottom sides of the PCV related hoses. I have seen many of that vintage with splits underneath causing idle/fueliing issues.
Look for a vacumn hose diagram and check all related hoses.

Went ahead and replaced the PCV hose elbows (the only rubber parts), and inspected the plastic tubing. I saw no issues with the plastic, but the rubber was questionable. No change though.

I have my mom's 2002 Explorer 4.0 right now, so I compared values on that. The IAC, fully warmed up, sits around 35-40% at idle. Given that information, and the lack of idle drop when I unplug mine, I either 1) have a vacuum leak the computer can't compensate for, or 2) the IAC is not fully closing

Inspecting the IAC off the vehicle shows that it does close, and spring pressure feels the same on both of them. Unfortunately, the IAC connector is 180 degree different between the two, so I can't put one on the other engine (same engine, but they use different intake manifolds). [I suppose I could rig up some wiring extensions, I may look into that]

The long term fuel trims you are seeing in your scan data do not indicate any type of a vacuum leak where the PCM is commanding the system to be richer. When you have negative fuel trims, that indicates the PCM is commanding the system to be leaner as it is already rich. (Please note your HO2S readings are hanging high in the 0.6 - 0.9 volt range) When the PCM is commanding the fuel trims to be leaner, you will see the HO2S's fluctuating / switching above and below 0.5 volts as they should be doing. Could you please show short term fuel trims along with the long term trims to get a better picture of what is happening? Also, is the PCV valve an oem valve or aftermarket? The reason I ask is I have seen some aftermarket PCV's have higher flow rates than the OEM's and can cause IAC issues. Has the oil been changed recently? Fuel dilution of the oil can also cause fuel trim issues as the vapors are brought into the intake manifold through the PCV valve. As a test of the PCV valve, plug it or disconnect the vacuum elbow from the intake plenum and plug the nipple. Does it now idle better? Also, does your scan tool measure MAF in grams / second? If so, your Ranger should be about 4 gms/sec. If it is less (ex.. 2.5 gms. /sec), your MAF is now underestimating air flow. Just something to think about.
Take care,
DougS

Hi Speedwagon,
Did you retain / write down your freeze frame date if there were any trouble codes? Please post that data.
I also noticed on your scan data prints, the ECT is only getting to 176*F. Was that the hottest it got or did it get closer to the normal operating temp of about 197 - 200*F? Also, have you tested your oxygen sensors to make sure they're operating properly? If you have access to a lab scope, that would be the best way to test them. Just like making sure the MAF is reporting air flow correctly, the HO2S's also need to be reporting correctly. Remember the old addage: Garbage in = Garbage out!
Take care,
DougS

About the IAC on these trucks: They can break internally as the plungers are plastic. They are also unable to be cleaned. If you have access to a like Ranger or Explorer with the same engine as yours, try swapping and note the results.
DougS

Forgot to get back over to this forum.

The Explorer of the same year has the IAC plug turned 180, and won't hook up without some jumper wire. Something I'd like to try, but haven't yet.

I'll check on the PCV and get back to this thread. I've also noticed, that as we get some warmer weather, it seems to misfire more while at a stoplight than when it's cold.

And on the ECT, it was hovering around 180F in the above screenshots. I can't say I've seen it go over that, but I'll verify that as well.

Oxygen sensors are cycling. Those I replaced, given unknown age and 200k miles. And with the Bosch factory replacement units.

IAC:
I swapped the IAC out with one from a 2002 Ex 4.0. The connector is 180, so I ran a small jumper wire. Same behavior. This makes me believe the ECU is seeing too much air, and is closing the IAC completely when warmed up. Disconnecting the IAC while running confirms this, as there is no change to RPM when warm, but drops a lot when cold. I clamped off the brake booster, and evap canister, and got no change in IAC%.

Temp:
The highest temp, while driving around was 178. Stock thermostat is 192F. So either my tstat is bad, or the sensor is bad. It's around 40-45F today, so there's no reason the engine shouldn't be reaching normal temps. Engine wants to go back to 170F when idling, and increasing the RPM while idling makes it get there quicker. An external temp sensor touching the tstat housing gave me 130F, so I'm inclined to think the tstat is the culprit.

Bringing this thread back, since I still haven't solved the issue. I've just been busy with other things.Just pulled the plugs, and did a compression check. Figure that's a good (re)starting point. Then I took some readings with Forscan desktop, instead of my phone. What I know, is that I have a higher than commanded idle, that is not smooth. I will often still feel misfires at stoplights. The IAC is commanded to 22%, which is closed. Attached are the condition of the plugs, and the oscope readings from Forscan

   
Link to full size graph

 

plugs look like they need changed. Some look like they got over heated from the bluing on them but also gap looks out of spec but not 100 % since it is a pic versus been in front of a gauge.

The plugs are fairly new iridium. But if they were overheated, what could be causing that? I still haven't found the underlying misfire issue yet, and it's still not throwing any codes.

On the topic of gap, well: Everyone on the ford forums swears up and down that 0.054" is the correct gap. The Haynes, and the owners manual, say that as well. The sticker under the hood says 0.062". So these are set to 0.054". And verified when I pulled them out. 

Hey Speedwagon, just from my own experience with a high idle on a Ranger with the 4.0, I feel like the TPS voltage is a little too high at idle there. This truck I'm referencing would intermittently stick at 1,200 or higher RPMs, and what I found was that the actual throttle plate shaft had worn and was physically getting stuck in a position that was not actually at fully closed throttle. Found that with scan data while monitoring the throttle position mode pid which shows either closed, part, or wide open. When this issue happened, that pid would show part throttle, and I was able to actually change the pid to closed by turning the throttle plate by hand by the linkage bracket. The TPS voltage pid would drop to around .85 when I fully closed it. With an actual RPM that does not match the desired, I would look into that possibility. There was actually enough excessive play in the throttle shaft that I could feel it rocking around slightly when I manipulated it. New throttle body cleared that issue up. Worth a look. Good luck.

Travis T.J. Harrison