Well here goes...High Idle woes!

[Jhummel73]

I have a fast idle, about 2k to 2.2k, at startup whether hot or cold, every time. If cold, idle will come down to1500 in about 5 seconds, then within a couple of minutes it will come down to normal IF I roll to a STOP. Thereafter it idles normally. If hot, engine will come down to a normal idle after a minute or two, IF I roll to a STOP, otherwise stays up until I come to a stop. After that, behaves normally. No CEL and no codes in the PCM

I have done the routine. I cleaned the IAC, cleaned the MAF, checked the throttle body, seamed reasonably clean, replaced air filter, disconnected battery for 15 min, checked electrical connections, etc. I have also disconnected the IAC, and the engine barely or won't idle, which indicates no leakage of air around the throttle plate and probably no vacuum leaks.

Some folks have said engine should idle fast at startup, but this is way too high and a bother.

Vehicle is a 2004 with 105, 000 miles and is in good condition. I have only had it for a few weeks. It is a 4.0 with manual.

When I come up with a problem, and gotta ask for help, it ain't simple!

 

[RonD]

Welcome to TRS

Idle RPMs are, of course, controlled by the computer, which uses the IAC(idle air control) Valve as a "controlled" vacuum leak to raise and lower RPMs.

Computer has "target" RPMs based on engine/coolant temperature, colder temp = higher idle.
That temp data comes from the ECT(engine coolant temp) sensor, on a 4.0l SOHC engine that sensor is on the thermostat housing.
It is right next to the ECT SENDER, the sender is for the dash board temp gauge only, SENSOR is for the computer only.

If you have a smartphone, or a tablet with Bluetooth, you can get an OBD2 Bluetooth reader for under $40, with this you can "see" what the computer sees for all sensors, also read codes.
This works on any vehicle sold after 1995, so not a bad investment, and its plug and play.

With this you could see what temp the computer is seeing on start up, could be bad ECT sensor or bad wire.
ECT sensor gets 5 volts from computer on 1 wire, its Return voltage on the other wire is what tells computer the coolant temp.
3volts is about 70degF
2volts 100degF
1volt 150degF
.5volt 200degF operating temp, lowest idle

If computer was getting 4volts from ECT at startup idle would be 1,800+

I suggest the Bluetooth reader because simply changing the ECT sensor($10) on this engine is a little more complicated than other engines.

Good how-to here on changing thermostat housing: http://bengrosser.com/howto/fordthermostat/

Page 3 has pictures of the ECT sensor and sender and how to remove them, they use clips, they are not threaded.


On manual transmission vehicles the idle will stay higher, approx. 1,000rpm until you come to a stop, it usually starts to drop when speed gets below 5MPH, that is an emissions software, RPMs will also stay high when shifting, usually last 3 to 5 seconds after clutch pedal is pushed in, again this is to lower emissions.
So this is "normal"

The excessive RPMs are not

 

[adsm08]

Ford had a TSB about high idle like that on the 4.0 with manual trans right around that year. The issue is resolved with a PCM software update.

 

[Jhummel73]

OK thanks for the info. I didn't realize the sensor wasn't threaded in. I do have the blue tooth reader on its way. Should be here early next week. Very curious about those voltages. Also, I did see that tech bulletin about the reflash of the software. Kind of afraid how much they charge for that, but may be necessary. I will try and keep you guys posted on further results.

 

[RonD]

The 2004 4.0l Ranger does need that reFlash, good call adsm08

In 2000 the Feds passed a Bill that required Auto Makers make Computer reprogramming software available to independent shops, NOT free, just available, so a Dealer is not the only one that can do it.
A shop needs a computer and Ford software, of course, and also a subscription to the Ford Data base to download the correct "new" Software/Flash to put on your computer.
Worth calling a Ford Dealer to get the cost first, then call a few independent shops to get their costs.


You do need to download the APP for the model of Bluetooth reader you ordered.
The OBD2 reader will show you if computer is getting correct temp from ECT sensor so will either confirm a problem with that sensor or wires, or take it off the table as the problem.
The temp is often shown as a voltage or in degrees Centigrade, you can usually change it to Fahrenheit in the APP settings.

If ECT looks good then you will need that reFlash

 

[Jhummel73]

Still waiting for my blue tooth code reader. Really want to get this cleared up before sub zero Temps hit here, probably November.

The fast idle is either longer or shorter duration based on engine temp, so it would seem the ECT is having some influence. I also pulled off the IAC and turned the key on and noticed it goes full open, but have read other forums saying that is normal.

I will check with Ford about reflash price and compare with some other garages if they are able to do it as well.

 

[RonD]

Yes, computer will open IAC valve all the way with key on, that's for starting, and why when you start any fuel injected engine RPMs should go high for a second or two then drop down as computer closes IAC Valve to set target idle.
So normal

 

[fr7]

Could this be the same problem in a 98 ranger 3.0 manual transmission? Sometimes the RPM will go way high when I shift to neutral or have the clutch down in gear, it revs up on its own and then slowly starts to drop down. What should this thing idle at when it's under normal operating temperature? It seems to be like 900 rpm is the lower it has ever idle since I've owned it, if I disconnect the IAC valve the engine sounds quieter but the RPM's stay the same, weird..

 

[adsm08]

No, you have air leaking in somewhere. If the engine does idle extremely low or stall with the IAC unplugged air is getting in where it isn't supposed to.

 

[fr7]

Mine doesn't idle extremely low or stalls, it stays the same, should I get a check engine light with the IAC unplugged? I yes, then there might be something wrong with it because I don't get CEL when I do it. I fixed a lot of vacuum leaks and can't find anymore, is there any special spots where this trucks like to leak in/out of?

 

[Jhummel73]

Update

I called Ford about the reflash and service manager didn't seem to think it would help but I scheduled it anyway. In the mean time I went to Auto Zone and bought their cheap IAC. Put it in and it didn't seem to work at all, because the engine barely idled and it was hard to start when cold. Besides, the electrical connector came out at a different angle and prevented me from putting the plastic engine cover on , so I took it back. Then went over to o'Reilly and bought a better one. This one looked like the original, but the engine basically behaved the same, but now goes to 2500 rpm on start, cold or hot, instead of 2200.

Finally went in for the reflash appointment today, but at the end of the day they called and left me a message, "vehicle ready to pick up, we didn't reflash because software was most current, no charge"

So..........still stuck with the apparent problem. I do believe it is a problem. Why would the engine start with the same idle strategy whether hot or cold? 2500 rpm for 10 to 15 seconds, then gradually drift to 1500, then after about 15 more seconds drop to 1000. Frustrating. I put the old IAC back in and will just live with it for now.

 

[RonD]

After engine is warmed up and idling, and you unplug the IAC valve the idle will drop to 500 or engine will stall, either means no vacuum leak.

You said idle stayed high, so there is a vacuum leak.
But first check throttle plate, pull off the large air tube from the upper intake to look at throttle plate, it should be closed tight, see if it is loose, push on it with your finger, open and close it a few times to make sure spring is tight so air flow can't hold it open.

Finding a vacuum leak
With engine warmed up and idling, and IAC valve unplugged, pull off 1 vacuum hose at a time from upper intake and plug that hole with your finger, you are looking for RPM to drop with that port closed.

Start with power brake booster hose and PCV system hose, the larger vacuum hoses.
PCV hoses are a known issue on the 4.0l SOHC, they crack at the elbows, the underside were you can't see it, adsm08 mentioned a while back that the early 2000's Ford vacuum hoses were starting to fail, crack, at around the 10 year mark, so you fall into that range


When you get your OBD2 reader check ECT temp voltage, could be ECT sensor is telling computer your engine is very cold all the time so computer has to keep idle high

 

[Jhummel73]

Sorry for the confusion but when I unplug the IAC the idle drops down to just barely running. Also I did get my obd2 bluetooth reader and ect appears to be tracking engine temp correctly.
I have mostly learned to live with this problem. I just have to give it a little time after start up, whether hot or cold, for the idle to taper down to about a thousand before I start to drive. Otherwise it will high idle until I reach the first full stop in my drive, then it drops to 750 and behaves normally.
The story Ford gave me is the computer won't allow reflash if it has the same version as the loading device. Anyway so they said.
Overall, it's still a great truck!

Sent from my SM-T550 using Tapatalk