1999 yukon high idle why

Check for trouble codes. You can get this done free at most car part stores.

unless you want to blow up the intake stop giving it gas before you turn it over what you are doing is dangerous all you are doing is dumping raw unburned gas into the bottom of the intake to the motor, one of these times you go to start it it will do this boom really loud then die, it will lift the whole back end of the vehicle off the ground, then if you try to start it again okay I edited the answer also could be your catalytic convertor plugged is the exhaust coming out good, change the sensors whatever you do stop pumping the gas if it wont start now get in as you need silence so shut the door and the radio off can you hear the fuel pump? it will sound like a huum for a few seconds if you cant there is your problem all I can say is stop pumping the gas as that's why its running bad you are burning out the sensors and all the computer code stuff and wasting expensive gas too. you prolly fouled your plugs as well.

throttle position switch sounds like getting false readings to computer,
incorrect volts or excessive play from the throttle plate or sensor causes this,has to be one or the other,also check for any intake leaks from the filter to the throttle body,good luck,Gary

Its cold start issues:----
Go through the list of help links mentioned below:----

Click the link :----

Cold start problem and vehicle shudder around 2500 to 3500 rpms
http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html
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Low idle when cold out side?
http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html
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Ford explorer 4.0 will not idle when cold?
http://technoanswers.blogspot.in/2012/02/ford-explorer-40-will-not-idle-when.html
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Automatic transmission shift lever hard to move on cold mornings?
http://technoanswers.blogspot.com/2012/01/automatic-transmission-shift-lever-hard.html
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Car won't start when cold?
http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-when-cold.html
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It can be issue with IAC( idle air control valve) causing the problem.

There are many other possibilities causing these idle issues. Engine idles rough.

There are few help links with solutions to troubleshoot such idle issues.

I suggest you refer the link below and follow its troubleshooting details:------

Click the link below:-----

Ford Expedition IAC valve replacing

http://technoanswers.blogspot.com/2012/12/ford-expedition-iac-valve-replacing.html

Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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Stumbling and stalling at idle after engine rebuild?

http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

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1999 Ford F-150 Idles rough and quits when gas pedal is pressed less?

http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms

http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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GMC Sonoma Stalls and idles low

http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html

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GMC Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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1996 Camry intermittent engine failure while idle?

http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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High Idle Problem

http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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High rpm in neutral? Inconsistant high RPM in neutral?

http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Vehicle stumbling at idle and shows code 54?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html

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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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These details will help.

Thanks.

There has to be a story about that situation

Share it with us ---the long version & what possibly
could we do for you ,IF --you never work on your
own cars,if that is the case

check the idle air control ( IAC ). it maybe sticking or it is bad. you can clean them out they get a lot of carbon from engine on them. hope this helps ! this is what controls idleing on todays vehicles. also be sure wiring is ok to the IAC. good-day !

Sounds like a sticky throttle if you can't keep idle. It won't hurt to try.... you can try a quick cheap trick by spraying a little carbon remover (buy at any auto store i.e. autozone, oreiley's) inside the throttle, open the valve, spray just small amount, close it back up and rev it a few times and repeat. It removes the carbon film after long use. fixed my idle issue in my cars. If its really bad you might have to clean it thoroughly but i highly doubt you have to do that.

https://www.youtube.com/watch?v=41yFXjibtLY

The computer has lost its memory for idle control possibly.Try this, crank the truck and shut is off.Do this as many as 20 times , each time try to leave it running for 2 or 3 seconds so you can see if it will idle on its own.Do this till it relearns base idle.

My quest 2004 idle below 500, start up then off, have to start couple times when the engine is cold. when i pushed the gas pedal, it smells gas.

Check your throttle position sensor