My engine has a high idle why?

Tiny
BRENT BASHAM
  • MEMBER
  • 2006 FORD F-150
  • 4.6L
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
Changed plugs and cops, truck ran great! A week later cleaned mass flow, still runs great but, now cranks at extremely high idle (2000rpms) Every time it's cranked!
Suggestions?
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Saturday, October 31st, 2015 AT 1:57 PM

35 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,938 POSTS
You may have an air leak at the throttle body or a problem with the IAC check this first. This guide can help us fix it

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

Please run down this guide and report back.
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Saturday, October 31st, 2015 AT 2:13 PM
Tiny
BRENT BASHAM
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Ok, I'll check. I didn't use a new gasket on the mass flow, (pretty dumb on my part) it's the only thing that was disturbed and probably where it's at.
I'll change this first and see if that fixes it.
Thanks for your info !
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Sunday, November 1st, 2015 AT 8:41 AM
Tiny
MHPAUTOS
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OK, good place to start looking, good luck with this.
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Sunday, November 1st, 2015 AT 12:29 PM
Tiny
RUSS39
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  • 1 POST
  • 2006 FORD F-150
  • 4.6L
  • V8
  • 4WD
  • AUTOMATIC
  • 138,000 MILES
So this only happens when the A/C is on and the truck is stopped at a light at idle. No codes are present. Spark plugs changed out 6 months ago. A/C blows really good, refrigerant is full. No other issues when driving. Any help well be grateful appreciated.
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Wednesday, May 5th, 2021 AT 12:22 PM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
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Good morning,

The idle air control motor is supposed to adjust engine RPM according to load. When the motor sticks or does not work correctly, this will result.

You cannot clean this motor as the dirt is in an area you cannot access.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

It is located behind the throttle body on the neck of the upper intake plenum. It attaches with 2 8mm bolts and an electrical connection.

I attached a picture for you of the location.

Roy
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Wednesday, May 5th, 2021 AT 12:22 PM (Merged)
Tiny
DBAUER78
  • MEMBER
  • 1 POST
  • 2002 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
The vehicle will suddenly kick into very high idle (over 3 rpms) and will not 'kick' down, but, it will only move at maybe 12 miles per hour. I don't know if this is engine or trans problem. The last time my husband 'banged' around the engine (most things are tested this way, to my dismay) but it did stop. We took it to a mechanic who could find nothing wrong and it has now happened again. I will have it towed to a dealer (?) But would like to know if you have any suggestions as to what would cause this?
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Wednesday, May 5th, 2021 AT 12:22 PM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
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For starters scan the PCM (computer) for codes

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If the PCM sees a problem it will store a code that will help in diagnosing the problem, get back with the exact codes.Sounds like it could be the IAC (idle air control) sticking, but will need to be scanned as to why it wont go over 12 mph.
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Wednesday, May 5th, 2021 AT 12:22 PM (Merged)
Tiny
DICK SIMON
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  • 1 POST
  • 2001 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 11,000 MILES
I changed the throttle body, lots of parts looked for vacuum leaks. Can I check my timing on this pickup with a timing light?
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Wednesday, May 5th, 2021 AT 12:22 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
Hello,

It sounds like you have an IAC motor that needs replacement. Here is a guide that will help you get the job done and some diagrams (Below) to show what is it like on your car.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

I would double check the large vacuum hose, they like to leak at the rear of the engine.

Does the engine have an EGR valve?

Please let us know what happens.

Cheers, Ken

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Wednesday, May 5th, 2021 AT 12:22 PM (Merged)
Tiny
JEREMYHARRISON
  • MEMBER
  • 2 POSTS
  • 2001 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
My truck has high idle for 15 to 20 minutes. There are no codes at all. It seems may be related to coolant temperature sensor. I know where the cylinder temperature sensor, but I'm having a hard time locating the coolant temperature sensor.
I found some people talking about it possibly having a thermostat instead but I'm not sure. Would there still be a sensor?
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Wednesday, May 5th, 2021 AT 12:24 PM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
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Good afternoon,

Why do you think it is the coolant sensor? It does not control idle speed.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

You said you knew where it was but you want to know where it is? Please explain.

The sensor is located just under the intake manifold on the left front of the engine.

Roy

REMOVAL
1. Disconnect the battery ground cable.

2. Remove the bolts and the accelerator control splash shield.

3. Remove the Idle Air Control (IAC) valve electrical connector.

4. Disconnect the throttle bypass hose.

5. Remove the bolts and the IAC valve.

INSTALLATION
1. To install, reverse the removal procedure.
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Wednesday, May 5th, 2021 AT 12:24 PM (Merged)
Tiny
JEREMYHARRISON
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That fixed it thank you.
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Wednesday, May 5th, 2021 AT 12:24 PM (Merged)
Tiny
JOHNNY MILLER2
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  • 1 POST
  • 1997 FORD F-150
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 14,284 MILES
Just replaced the EGR valve, flushed radiator and oil change. Now the truck idles high! Need to know what do I need to check how to get idle down.
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Wednesday, May 5th, 2021 AT 12:24 PM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
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Good morning,

When you had the EGR off, were the passages clear of all carbon? If some carbon is in there and holding the valve open, it creates a vacuum leak and the idle will be high.

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

Also, remove the connector for the idle air control valve and see if the idle drops.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

I would also clean the throttle body of all carbon as well.

https://www.2carpros.com/articles/throttle-actuator-service

Roy
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Wednesday, May 5th, 2021 AT 12:24 PM (Merged)
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
Give the idle air control valve a tap with a screwdriver handle, these are notorious for sticking, and especially after a decarb service.
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Wednesday, May 5th, 2021 AT 12:24 PM (Merged)
Tiny
BOBBYB69
  • MEMBER
  • 37 POSTS
  • 1995 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 175,000 MILES
Hey guy's, i'm back. Happy New Year to y'all.

First I got an email saying I had a message from maryanne or annemary but never could find it.
Second my daughter's Kia has never acted up again. I'm confused.
Now to my Ford. I've replaced TPS, IAC and fan clutch but still having idle problems. When it's cold it starts and idles good but after it's hot and I start it. It revs between 1,500 and 2,000 rpm's really fast and then drops to normal idle. While I am driving and slowing down I have to shift into neutral and let the engine rev up really fast in order to get it to idle right.
In short what could be causing the strange situation. Also some days it runs pretty good. Thanks for all y'alls help.
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Wednesday, May 5th, 2021 AT 12:25 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,014 POSTS
Hi,

It sounds like you have already done a lot. Have you checked for engine vacuum leaks? Also, have you checked to confirm fuel pressure is within spec?

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know if you found any diagnostic trouble codes also.

Take care,
Joe
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Wednesday, May 5th, 2021 AT 12:25 PM (Merged)
Tiny
TOUGHDIVER
  • MECHANIC
  • 224 POSTS
Hi,

The engine needs an air source to run faster. Either the throttle is not returning or the engine is getting air from another source.Check the throttle Cable, IAC/Auxiliary Air Valve and Cruise Control engagement, PCV valve hanging open.Check for an overheat situation - PCM commands faster idle for attempted cool down.High idle after driving for a while and slowing for a stop, idle speed increases. After driving for a while and slowing for a stop, idle speed increases. Makes me think the brake booster is faulty and once in a while the seal hangs open and allows atmosphere air into the vacuum side which would raise the engine speed and at the same time make it harder to brake.Put a vacuum gauge on the booster between a check valve and the booster and step on the pedal periodically after running engine to build vacuum before each
attempt.The booster should drop vacuum but still have some left for a second attempt.

if not, and it bleeds down, it's bad. Note: On vehicles that have curb idle speed adjustment capability, An idle speed that is too high will cause vehicle to creep, have harsh engagements and harsh closed-throttle downshifts. On vehicles equipped with an Exhaust Gas Re-circulation (EGR) system, it is important to check the system for proper operation. The Manifold Absolute Pressure sensor, Mass Air Flow sensor, and Coolant Temperature sensor can cause intermittent high idle also. Try unplugging one at a time see if it makes a difference in the RPM's. I'm attaching repair guides below. Let us if you more assistance.

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

Thank you
Joe Terwilliger
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Wednesday, May 5th, 2021 AT 12:25 PM (Merged)
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
We need to start with checking for codes. The fact that you replaced the TPS is good but we could still have a wiring issue or control module issue. Basically if we have codes we can chase that down but if there are no codes then we will need a scan tool to see what the PCM is seeing as the TPS signal voltage. Engine off with a closed throttle, it should be around 1 volt. If the PCM is seeing something different then that points to the issue. At that point, we need to monitor the voltage on the 3 wires are the back of the sensor. You should have ground, 5 volt reference, and then 1 volt on the signal wire with the engine off and throttle closed.

Since the sensor is new, I suspect this is what you have. At that point, if the PCM is showing a different voltage for the TPS then we know either the wire is the issue or the PCM is faulty.

Lastly we need to check for a vacuum leak just to rule that out.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if you have questions and we can go from there. Thanks
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Wednesday, May 5th, 2021 AT 12:25 PM (Merged)
Tiny
USMC1833
  • MEMBER
  • 1 POST
  • 1995 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • MANUAL
  • 129,000 MILES
Truck starts fine and idles fine as well at start up. Engine rpm will suddenly increase to 2,300-2,500 rpm's without touching anything. When at that high rpm all I have to do is shift gears and it will literally drive itself from a stop up to about 55 mph. I reduce the speed and the second I push in on the clutch, it will jump to 2,500 rpm's and stay there until I put it in gear and the transmission brings the rpm down accordingly with the gear/speed. I have found no vacuum leaks, no check engine light has come on, I have replaced the IAC three times and even recently bought a Motorcraft IAC and put that in but it continues. Which steps should I take next? Do I need to reset the DCM, can I? Or re set the IAC? The idle screw is good. Set to about 900 rpm's. When it idles high, the throttle cables remain in the same place. So I have no earthly idea. Can someone please bestow some knowledge?
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Wednesday, May 5th, 2021 AT 12:25 PM (Merged)

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