1989 Idle issue
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Junior User
Joined: Apr 2003
Posts: 98
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From: Virginia
1989 Idle issue
I have inherited a 1989 bronco with 351. Idle issue it has is as follows. When you start the truck, it idles ariound 1300 RPM. Then it will fall to 800. When you leave home and get to work and place it in park or neutral, it shoots up to 1300 or 1200 RPM and stays there. If I cut the truck off and restart it right away, it idles at around 800 RPM. After work start it up idles 800. Go home back in driveway, place in park....it goes up to 1300 RPM and stays there. Took it to mechanic, idles perfect when I am there. He replaced throttle body and EGR valve w/sensor. Still has same issue. Any input, ideas or fixes would be welcomed. Thanks.
Postmaster
Joined: May 2007
Posts: 2,757
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Mine does the same thing, I have been told the Idle air control valve being faulty, or dirty will cause it to do that. I tried cleaning mine, it made a little bit of a differance, but not much. Mabey I need to clean it some more.
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Pull codes before going ANY further... you are chasing a phantom otherwise.
It could be any number of things from a simple vacuum leak to a failed EGR valve or exhaust gas checkvalve. Idle is controlled by the computer and ANY mis-information getting back to it will cause idle issues.
It could be any number of things from a simple vacuum leak to a failed EGR valve or exhaust gas checkvalve. Idle is controlled by the computer and ANY mis-information getting back to it will cause idle issues.
Cargo Master
Joined: May 2004
Posts: 3,007
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The first thought to cross my mind would be the engine coolant temperature sensor. If the computer thought the engine was cold, it would increase the rpm to heat up the engine faster. Check the cooling system for leaks, level, liquid quality.
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Junior User
Joined: Apr 2003
Posts: 98
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From: Virginia
We did get an EGR sensor code at first. We replaced the EGR valve with sensor (only way you can get used one). Now their are no codes. We replaced the EGR valve and sensor the same time we changed the throttle body. Niether made a difference on the idle issue.
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