idling too fast

Any codes in the PCM? What work besides the IAC has been done to the truck?

This guide can help us fix it

https://www.2carpros.com/articles/engine-idles-too-high

Please run down this guide and report back.

There are no codes, Truck has only been tuned up ,, plugs and wires.......

So it only does it sometimes? What kind (brand) of IAC did your mechanic use?

Engine Performance problem
1999 Ford Ranger 6 cyl Four Wheel Drive Manual

hi.i have a 1999 ford ranger 4.0l ohv with 5 speed manual trans.Sometimes when coming to a stop and pressing the clutch in,the rpm's will hang around 1300-1500 and then slowly drop back down around 800.I have a scan tool and noticed that when i release the throttle no matter what the rpm stays at the tps pid always reads around 18.4%.To me that says the throttle plate is closed and not hanging up.LTFT and STFT read in the correct range(between -10%-+10%)
but the maf when the idle hangs up reads 1.1lb per mile,when it idles normally maf reads .55lb per mile.This is a new maf sensor from napa.Is this a defective new maf sensor or am i barking up the wrong tree.Also i know there is a t.s.b. for this but i cannot find the calibration code in the usual places to see if my vehicle is affected. Thanks.

Have you checked the IAC?

yes,tried new one and did the same thing.But if i drive with the iac valve disconnected rpm drops normally.

I would recommend trying a different MAF. You could have gotten a bad one.

While I'm driving, every time i take the truck out of gear it revs up to about 3,000 rpm unless i come to a complete stop where it will fall back down to 1000 rpm. i replaced the throttle control sensor on the throttle body. It was driving fine after that but then leaving the truck sitting for a week the problem only came back. Also trying to start is a problem unless your foot is down all the way on the gas pedal.

Has the check engine light come on?

Thanks i will try that.

no the check engine light has not come on..

Let me know if it helps.

It sounds like a bad throttle position sensor, but I can't be sure without the check engine light. Therefore, start by checking for vacuum leaks.

Let me know what you find.

Joe

my problem turned out to be a leak in the lower gasket under the pental on my 95 4.0 ranger, the dionostic cost me 150.00$ they wanted 500.00 to fix it,i bought the book and fixed it myself for twenty bucks.

Hello, When started engine idles fast then slows down, but it doesn't seem top be enough. Used to get 21 mpg, now get 16mpg.

You could try to clean your IAC valve, it may help with your idle problem and your poor fuel consumption. Also check your IAC motor.
I would also clean the MAF sensor, replace the air filter, inspect/replace the spark plugs and the whole ignition... in a nutshell get a tune-up. It should help with your fuel economy.

That could be the problem with this one too. Vacuum leaks cause all sorts of problems.

When the cluth is disengaged and the truck should be decelerating the idle races untill the truck comed to a stop. Happens intermitintly aslo if I punch the gas pedal real quick the idle returns to normal. Have also experienced the idle throttling up by its self.

There is a vacum hose on the valve cover next to the oil fill that runs up to the throttle that was dried and loose. Changed the hose with a new one and 2 hose clamps and the problem stopped.

My ranger was running ok when I took it to a Ford Dealership to replace a leaking valve cover gasket. The throttle body was removed and cleaned also. Now when you accelerate and then decelerate the idle will not come down as it should it may take 10 to15 seconds for it to idle back down. It will do this each time whether it is hot or cold .The IAC valve has been changed twice. What else can it be? Lash Formby

First, I'd take the truck back to Ford and at least let them know that you're having problems with the work they performed. Then I would check the return spring and the throttlebody plate to make sure that is not jammed up with something or a spring is missing

my engine often idles very high. sometimes when i drive, it idles so high i can do 5 mph or so without pushing on the gas pedal...very often when i come to a stop the engine idles VERY high for 5-10 seconds then comes back to a normal idle. i have replaced the idle air control valve....but it did not help. what is causing this and what do i need to do ???

earl scott

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.

I have a 98 ford ranger 2.5, 2 wheel drive, 5 speed manual. And sometimes i shift gears, pull up to a stop light or stop sign with the clutch pushed in, the engine revs up for a minute or so unless i shut it off and turn it back on or i engage the clutch. It soes this every now and then and i cant figure out why, the check engine light isnt even on. Please help!

Clean out the idle air control valve, clean MAF sensor with an approved cleaner and test the throttle position sensor.

3.0 L
car runs and drives perfectly.

but when, and only when i turn the a/c on, or turn on a climate control function that requires a/c, the idle goes through the roof to 2,000 rpms and stays there like a cruise control.

sometimes in the morning if its not terribly hot out the problem doesnt happen. the a/c is properly charged and blows cold. i have replaced the idle control valve, and to rule out a possible vacuum leak i drove the car with the IAC removed and the IAC intake holes plugged. the problem didnt happen then. i have studied my ford service manuals searched the internet, asked friends, and got nowhere. seems like a rare problem. i also scanned the obd and have not found any codes nor has the check engine light ever came on.

Hi zawartkay,

Thank you for the donation.

Problem is related to the IAC and it could be :

1. Faulty ECM. The engine control would increase the voltage to the IAC to open it more when the A/C is turned on. The higher the voltage the more the IAC would open.

2. Wrong temperature signal. The ECM could be receiving the wrong signal from the Engine Coolant Temperature sensor and increase the idling speed when it thinks the engine is still below operating temperature. This could be due to a faulty ECT.

thank you for the reply.
i tested the ect with an ohmeter and at normal operating temperature it is 2.5 k ohms.

also, when this problem happens the engine overheats, which i am guessing is a fuel/air mixture problem as a result of the iac is being told to open too much.

if i go out and drive the car and never turn the a/c on it is fine. but after running the a/c and experiencing the problem, if i turn the a/c off, the problem still occurs and will not go away until i shut the car off and restart it.

if i am running the a/c and experiencing the problem, ocassionally if i stop at a light, it will go away, then when i get moving again and work the gas pedal a few times it will come back.

i always thought a pcm rarely goes bad.

PCM rarely goes bad but the still do.

Since you have overheating issues, then that is the most likely cause.

Have you checked the coolant in system?

Is the IAC equipped with coolant hoses?

coolant level is normal, no the iac does not have coolant hoses, only an electrical connection.

is there any possible circuit that is on when the a/c is on that tells the pcm to increase the idle? could this circuit be giving the pcm too strong of a signal causing the problem?

otherwise i would agree the problem has been narrowed down to the pcm.

this was previously a florida car and has seen tremendous a/c usage.

97 ford ranger starts and drives fine except when i coast to a stop the idle stays revved up a bit, then when i come to a full stop it settles down to normal. I'll take off, go to shift and the engine revvs up some, i'll shift gears, let out the clutch and the truck sort of lunges a little bit. It revs and idles high then settles down to normal again.
No engine light has come on.
I'v looked under the hood for loose hoses, clamps etc...don't see anything noticible.
Read online about the EGR valve, oxygen sensor, Idle speed control motor and have identified all of those componens but i don't know what exactly they do or if
any of them need to be replaced.
Appreciate any help

Inspect and test the idle air speed control motor/valve and throttle position sensor

When A/C or other electrical components are turned on, the additional load would cause the engine rpm to drop.
This extra load is detected by the PCM, which would compensate by increasing the air intake via the IAC.

If it is the electrical load detector, then the rpm would also increase if the headlights are turned on.

As the IAC is not equipped with any coolant hoses, the ECT would inform the PCM the engine temperature. If the reading says the engine is cold, the IAC would increase the idling speed.

PROBLEM SOLVED!

Since there was no check engine or code thrown I figured it might be mechanical.
I started the diagnosis with simple tune-up procedures.
Changed all the spark plugs and that solved the problem.
Now...runs like normal.
Thanks for the timely and good ideas!

what has happened recently is the idle would be doing this at all times. i have read the article about high idle where it says

"I can tell you this, the oxygen sensor (02), MAF or MAP and coolant sensors are prone to this type of sensor failure."

what happened the other day is this:
i finally got a check engine light. pulled into vatozone
and this is what it said. p0420, catalyst efficiency below threshold bank 1. perhaps my o2 sensors, or catalytic converter may have been causing the computer to run in "open loop mode" or "closed loop" not sure which one, but a high idle condition.
is this a possibility?
i suspect this has been causing my problem

thanks!

My '96 ranger has similar problems. The idle willl jump to 4000-6000 RPM while in nuetral, or with the clutch disengaged. The only way to bring the RPM down is to lug the engine or fry the clutch... Any other advice would be very much appreciated! Thanks

P0420 is usually a fault with the catalytic converter.

For the idling to increase, something has to work to allow increased air flow into the manifolds and the O2 sensor is not likely to be the one. If the MAF is faulty, it wuld usualy stall rather than increase the rpm as it needs increased air flow otherwise it would be running rich.

Have you checked for intermittent restrictions to the throttle body ? Somthing that might cause the throttle to remain partially opened?

I don't know alot but i'll tell you what worked in my case.
If you have a check engine light, hook up a computer reader and identify the code. That should point you in the right direction. Mine had no "check engine" light, so i started with simple tune up stuff. All I did is change my spark plugs. A smarter guy than me told me if the plugs are worn out then the truck has to enrich it's fire/fuel mixture at idle to stay running. My plugs were 30,000 miles old and it worked like a charm. Consider changing the plugs & look at the tips & wire ends for corrosion, (white or green powder.) If mine still ran rough i would have moved on & changed the plug wires & fuel filter.
Let me know how it turns out.
River

you are not going to believe what the problem was and it couldnt be guessed a hundred times. the battery!
the battery was old as hell. it was unable to team with the alternator and support the a/c compressor load, plus cabin fan high load. so the computer goes into some kind of rescue mode, and cranks the rpms. but it went so haywire. the computer would tell the iac to go full blast.
replacing my battery and spending the 90 bucks was the magic pill! my electrical system can now support the a/c and
it now idles so perfectly i can engine brake, and shift smoothly.

thankfully the only other money i've thrown at the problem has been on:
4 huge ford factory service manuals, a multimeter, and a mass air flow sensor.
oh and the iac valve i bought but then used and returned cause it didnt fix the problem. vatozone!

well i really feel great that i didnt go buying a new ECM. because i was coming really close to narrowing everything else down and renderring out all other possibilities.

i just cant believe that the battery was the culprit.
please pass this along and put it in your tech section or
things to check first section.

Thaks for some direction. I started with a tip from a buddy, and removed the throttle body and upper intake, cleaned them out really well, replaced the gaskets and reassembled. while I was at it, I replaced the EGR valve and this seemed to DRASTICALLY improve the performance. IMy next move is to actually buy a code reader, and tackle the other issues one at a time. I will most definitley be doing the tune up, and replaceing all parts as needed. Again thanks for the time to reply!!