Engine accelerates on its own and won't idle
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Junior Member
Joined: Mar 2011
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Engine accelerates on its own and won't idle
In cold weather -27 degrees Celsius( -17 Fahrenheit) my truck starts up properly and idles properly and I warm it up for a good 15 minutes, after driving the truck for an hour I noticed that my truck was accelerating on its own. I thought that it was the cruise control , but applying the brakes and
turning off the cruise control did nothing. I then put the truck into neutral and the engine revved up to over 4,000 rpm. I then turned off the ignition
and coasted to the shoulder of the road. On the side of the road I disconnected the cruise control wires going to the brake cylinder and then started up the truck and then it immediately started to overreving .I quickly
pumped the gas pedal a few times and the engine finally idled down.
turning off the cruise control did nothing. I then put the truck into neutral and the engine revved up to over 4,000 rpm. I then turned off the ignition
and coasted to the shoulder of the road. On the side of the road I disconnected the cruise control wires going to the brake cylinder and then started up the truck and then it immediately started to overreving .I quickly
pumped the gas pedal a few times and the engine finally idled down.
Senior Member
Joined: Jun 2009
Posts: 3,592
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You will need to replace your Idle Air Control Valve. Very easily located as it is the shiny cylinder with two bolts on the end of it on the top of your intake.Unhook your negative terminal on your battery and then remove the connector, two bolts, and gasket from the IAC. Then replace obviously and hook up the battery and it should be good to go. Good luck!
Senior Member
Joined: Jul 2007
Posts: 3,291
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From: Beaverton Or.
Depending on the year, make sure your cruise recall has been done also. But yeah, I would inspect the throttle body at the butterfly valve and also the throttle cable while the engine is off. Make sure it is going back to closed position. There should be some slack in the throttle cable at the throttle body when it is fully closed. Rotate it with your hand and see what it is doing. The cable may be binding up somewhere or the valve may be hanging up due to carbon build up.
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Comment:
...The only way a 4 cycle engine will accelerate is by air flow into the intake.
Not fuel or for any other reason.
You have a condition that is allowing uncontrolled airflow into the engine.
Fuel and ignition added is only the way the air is forced to expand to push on the piston.
Do not drive the truck again until you go over all the reasons for uncontrolled air.
Clean or replace the intake air control device, clean the throttle body plate and inside of the throttle body, check for loose bolts holding the throttle body on and it's conncting part to the intake manifold and check all intake hoses subject to vacuum as well as a good check for throttle cable hangup both throttle and cruise control..
.
Good luck.
...The only way a 4 cycle engine will accelerate is by air flow into the intake.
Not fuel or for any other reason.
You have a condition that is allowing uncontrolled airflow into the engine.
Fuel and ignition added is only the way the air is forced to expand to push on the piston.
Do not drive the truck again until you go over all the reasons for uncontrolled air.
Clean or replace the intake air control device, clean the throttle body plate and inside of the throttle body, check for loose bolts holding the throttle body on and it's conncting part to the intake manifold and check all intake hoses subject to vacuum as well as a good check for throttle cable hangup both throttle and cruise control..
.
Good luck.