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  #1  
Old 01-06-2017
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idle issues 2008 2.3 manual transmission

ok here is the situation with the idle and i have looked around and not found any ideas. truck starts fine and runs fine. but say i am coming up to an intersection and i shift into neutral and coast the idle stays around 1200 rpms till i come to a complete stop. i had a s10 and that did not happen at all. even if i come up to a red light and push the clutch in the rpms are at 1200 for a few seconds then they drop to around 800 where it should be. i read something about reflashing at the dealer but it was not a idle issue. its a 2008 2.3 with the 5 speed manual tranny.
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  #2  
Old 01-06-2017
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My 3 litre is the same way, the computer holds a high idle for a number of seconds and then drops to around 800/950 rpm.
Apparently its supposed to help with the reduction of emissions.
Has yours always behaved this way or did it just start doing this ?
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  #3  
Old 01-06-2017
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it has been that way since a bought the truck a year ago. i sprayed the intake, iac, cleaned maf, new o2 sensor.
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  #4  
Old 01-06-2017
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For now, unless someone else chimes in, I'm going to say that's the way it's supposed to be.
After the truck is fully warmed up, unplug the IAC valve, if the idle drops and the truck almost stalls, that tells you that the IAC valve is working.
You may get a code for "low idle", but you can disconnect the battery for around 15 or 20 minutes to get rid of that.
It will still be there in the computer, but the dash light will be off.

Last edited by Jeff R 1; 01-06-2017 at 10:57 PM.
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  #5  
Old 01-07-2017
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thanks, i was checking into iac valves and i was going to try that
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Old 01-07-2017
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Jeff R 1 is correct.

The high idle while slowing down to stop is normal. Also, you'll see that the RPM's kind of hang while you are in the middle of a shift. This is all done for emissions reasons. The idle may be a bit higher during the winter vs. warmer seasons.

I know that Jeeps do this as well. Here's the description of how this works for a Jeep (and I suspect Ford has something similar as well):

"The speed sensor generates 8 pulses per sensor revolution. These signals, in conjunction with a closed throttle signal from the throttle position sensor, indicate a closed throttle deceleration to the PCM. When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received). Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value. Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed."

Now, if you coming in hot and stop with the clutch pushed in and the idle stays at 1200-1500 while you are stopped Then it may be a sticky IAC or TPS.
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Old 01-07-2017
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thanks so much, the more i look into this it may just be a factory thing. i did unplug the iac and it stalled so it is working. when i come to a light and push the clutch in it drops to around 1100 then drops to 800 rpms. i am so use to the engine holding you back a little when you go down a hill because the engine is not pushing you where as the ranger would because its putting fuel to keep the rpms above idle if i am thinking this out right. the reason i say this is if i am going down a hill and push the clutch in whether its 15 mph or 35 the rpms drop to about 1100. as soon as i stop it drops again.thanks
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Old 01-08-2017
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Make sure you use maf sensor cleaner. I used brake cleaner and starting fluid and neither one worked. Another idea is to remove iac and clean thst. I had mine off twice and got more gunk with a q tip the second time.
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  #9  
Old 01-10-2017
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high idle

just to add to my post , when i am at a stop light on a hill the rpms are around 800. the light turns green, no traffic i just start coasting down hill in nuetral the rpms start to go up to around 1000-1100 till i stop again. i figure the iac has to be connected to the speedometer in some way. i can see it have to do with emissions coming to a stop but it shouldn't do it from a stand still and start coasting. any ideas? thanks
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Old 01-11-2017
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I still don't think it's a problem.

I have a long, steep hill just about 2 miles from me that I will test this on, on Sunday (my first day off work). It's steep enough to get going with no throttle input. And I should be cruising pretty fast by the time I hit the bottom of it. I suspect the idle RPM will be higher.

Also, although I don't have access to any of the service manuals I did find this info regarding the IAC and PCM:

Quote:
The idle air control (IAC) valve assembly controls engine idle speed and provides a dash pot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm.

The PCM uses the IAC valve assembly to control:
- No touch start
- Cold engine fast idle for rapid warm-up
- Idle (corrects for engine load)
- Stumble or stalling on deceleration (provides a dash pot function) <---that one I believe is where we get the increased idle RPM while rolling with the clutch pushed in.
- Over-temperature idle boost.
- Air Assist to Injectors.
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  #11  
Old 01-16-2017
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Ok, I tested this yesterday on two hills.

The first smaller hill I was doing about 40mph. I crested it, pushed in the clutch and the idle stayed around 1000-1100 rpm until I came to a complete stop. Then it dropped down to the 700-800 range.

On the second much steeper hill I actually stopped completely. I let the idle drop to 700-800 and then pushed in the clutch and let the truck coast on it's own. I did not use the gas pedal the entire time. Right as the truck started moving the idle went up to 1000-1100 RPM and stayed there. By the bottom of the hill I was coasting at 55 mph (still not using the gas pedal) and the RPM's were still 1000-1100 RPM. And when the truck finally rolled to a complete stop the RPM's dropped back down to 700-800 RPM.

So, the IAC (and probably other sensors) also use the VSS sensor to adjust idle.
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  #12  
Old 01-31-2017
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My 06 does similar. Coasting maybe at 1000-1100 rpm and will drop to 750-800 when I stop. Been like that since the day I bought it 6 years ago with 49k miles.It hangs for a second for you to shift too. It is normal. Frst vehicle I have ever had to do that but makes it easier for people that are not use to a manual to drive also.
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  #13  
Old 02-01-2017
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its weird, but if sitting downhill and just start to coast in neutral the rpms pick up. on well
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  #14  
Old 03-11-2017
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Check the throttle body butterfly plate. If there is a gap around the outside edge that will cause the problem.
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  #15  
Old 03-11-2017
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Newer vehicles with manual transmissions will hold RPMs high when shifting, that helps lower emissions, not to help newbe manual trans drivers.
RPMs will also stay high if coasting, clutch pedal in or in Neutral, until speedometer drops below about 5MPH, also for lower emissions.

To help your MPG with manual trans, you shouldn't coast with clutch in or in Neutral down a hill.
With fuel injection it is possible to shut off the fuel injectors when coasting, and computer will do this if TPS(throttle position sensor) shows closed, "foot off the gas pedal", and engine RPMs around 1,500 or higher
Computer will restart injectors, at idle levels, when RPMs drop down under 1,500.

So leave it in gear when you are going down hill, to get those injectors to shut off

In the old days with carbs you wanted to lower RPMs because at higher RPMs even with throttle closed you were sucking more gas out of the idler jets, because of increased vacuum in intake manifold.
Thats old school thinking and was correct

Fuel injection is better, 0 fuel used when throttle is closed and RPMs are above 1,500
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  #16  
Old 03-12-2017
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thanks, i understand the emissions part, just thought it was strange that the ford was the only one to do it on my last 3 vehicles with a manual
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  #17  
Old 03-12-2017
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Would depend on the emissions of that engine and that years requirements.
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