You could have a problem with the throttle cable.Inspect the cable that connects the foot pedal with the throttle body to make it go "zoom, zoom". Its also possible that the inside of the throttle body is gummed up with dirt, dust, varnish and soot. Clean the throttle body with throttle body cleaner liquid available at local auto parts store.Take off the air intake hose, and spray everything inside there until it is clean and shiny. Be aware you may have trouble starting it the first time after cleaning.But once it starts and runs properly,then for second time it will run smooth like before.
Other possibility is vacuum leak.
To access the vacuum leak method by professional mechanics is use starting fluid. Simply spray around the engine with it running ( not on the exhaust ) and listen for a change in engine noise. Once You have found the area, turn the engine off and check for cracked vacuum hoses or leaky gaskets.
This will help.
1996 Camry intermittent engine failure while idle?
Engine quits at idle?
http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html
Car overheats and Air blows hot at idle?
http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
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
2004 ford freestar van idles rough?
http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html
Ford explorer 4.0 will not idle when cold?
http://technoanswers.blogspot.in/2012/02/ford-explorer-40-will-not-idle-when.html
Ford runs lean and idles rough?
http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html
Engine stumbles coming off idle when warm?
http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html
Erratic idle on car?
Car dies when gas pedal is pressed?
Low idle when cold out side?
http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html
GMC Idle Air Control (IAC) Valve Replacing?
http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html
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
But if that is not helping,then problem is faulty TPS.Throttle position sensor located in throttle body.
To see how throttle body looks,see the image shown below :----
Also there is IAC idle air control valve motor on throttle body.If it gets dirty,the same problem will be noticed.Try cleaning the idle valve first and see,if that is not helping,then it has to be replaced.
To access the vacuum leak method by professional mechanics is use starting fluid. Simply spray around the engine with it running ( not on the exhaust ) and listen for a change in engine noise. Once You have found the area, turn the engine off and check for cracked vacuum hoses or leaky gaskets.
This will help.
Thanks.
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