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Adjusting Idle Speed 

 

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 Post subject: Adjusting Idle Speed
Posted: Thu Sep 18, 2008 8:08 pm 
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Trying to find a doco or something that will explain how to change the idle speed. I read somewhere ages ago that you have to remove something like the ISC? Dunno where that is though... can anyone direct me to a site or bit of info on adjusting the idle speed on an EL falcon or just give me a quick run down?
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Posted: Thu Sep 18, 2008 8:12 pm 
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usually its just a screw near the throttle body

 

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Posted: Thu Sep 18, 2008 8:14 pm 
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i found one that is just above the throttle body in close proximity to the throttle cable too but thought it might have been a screw to adjust the air/fuel mixture but that is all controlled by the ECU isnt it?

a doco would be great if there is on floating around somewhere?
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Posted: Thu Sep 18, 2008 8:18 pm 
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i belive the air/fuel is further back but i may be wrong

 

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Posted: Fri Sep 19, 2008 9:12 am 
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its not the black knob ontop of the ISC its a screw a little bit further down from memory.

someone might have a good picture of it for ya

 

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Posted: Fri Sep 19, 2008 10:29 am 
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dont know if this helps but on the early E series its a screw on the under right hand side of the throttle body which has a spring (?) on it. dunno if they have similar setup on the BBM though...sorry if this means nothing. i'd check right now for you if i owned one.

 

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Posted: Sat Sep 20, 2008 12:28 am 
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1) Remove ISC plug and place 0.75mm feeler gauge in between stop tab and throttle lever.
2) Put engine in diagnostic mode. Short far left top and bottom pins on plug and start engine.
3) Now wait approx 2mins until the engine stumbles and check to see whether the engine idle is at 700rpm(+-50rpm)

If it is not within specs then just turn the throttle blade adjusting thread screw with a small flat blade screwdriver. It helps putting the dash in diagnostic mode so you can get a digital readout of the tacho if you like this process being very accurate.

cheers.....................

 

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Posted: Sat Sep 20, 2008 12:29 pm 
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EL__Fairmont wrote:
1) Remove ISC plug and place 0.75mm feeler gauge in between stop tab and throttle lever.
2) Put engine in diagnostic mode. Short far left top and bottom pins on plug and start engine.
3) Now wait approx 2mins until the engine stumbles and check to see whether the engine idle is at 700rpm(+-50rpm)

If it is not within specs then just turn the throttle blade adjusting thread screw with a small flat blade screwdriver. It helps putting the dash in diagnostic mode so you can get a digital readout of the tacho if you like this process being very accurate.

cheers.....................


Spot on EL_Fairmont but the engine must be at operating temperature.
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 Post subject: Re: Adjusting Idle Speed
Posted: Sat Aug 14, 2021 9:03 am 
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Does anyone know why the engine needs to be at operating temperature for setting base idle?

My issue is an unstable cold idle, and wonder if setting base idle when cold could help.

I understand the ECU and IAC do the finesse work above base idle, but isn't the worst idle case in my situation when it's cold? (high friction, low combustion chamber temp, more difficult combustion environment).

If we're setting base idle for when the engine is warmed up, doesn't that ask a lot of the ECU during warm up where it will have to get the IAC to constantly avoid stalls or low idle?

Old thread, but hoping someone's watching!

Cheers.
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 Post subject: Re: Adjusting Idle Speed
Posted: Fri Sep 10, 2021 11:51 am 
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When the engine is cold, there is more fuel that does not vapourise/atomise enough to burn. Less fuel available to combust means less torque - not enough to idle at the desired RPM, so the ECU is programmed to add fuel (lower AFR) when the engine is cold. As the temperature comes up, the amount of fuel added is reduced. But the extra fuel won't be much help without extra oxygen to burn with - thus, the IAC.

Adjusting the idle screw just lets more air in, and the ECU adds more fuel to match. If you set the idle screw for a certain RPM when cold, with no added IAC air, it will idle at a too high an RPM when the engine warms up and more of the fuel is burned, producing more torque. In this situation, it is the throttle plate opening (idle screw) that is setting the minimum amount of air, and there is nothing the IAC can do to reduce that volume.

Base idle is set on a warm engine, with IAC disconnected, and it is set to an RPM slightly lower than your desired idle RPM. This allows the IAC to operate within its available range. To get up to the desired idle RPM, the IAC doesn't have to open much when the engine is warm, but must allow much more air through when the engine is cold. Yeah, that's asking a lot of the IAC, but that is what it is designed to do.

Hope that helps.

BTW, there can be many causes of an unstable idle - dirty throttle body, IAC or injectors, vacuum leak, spark plugs dying, ECU capacitors drying out, etc.

 

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