High idle
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Mountain Pass
Joined: Oct 2002
Posts: 206
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From: Jaqcksonville
High idle
Van started this last week. After shut down then restart engine revs to 1500 or so for about 5 secs then slowly drops to idle. The wait is a pain as the idle is too high to put in gear. Cleaned air bypass, checked throtyle stop etc all ok. Any other ideas
Post Fiend
Joined: Apr 2005
Posts: 5,720
Likes: 5
From: Washington state
"Cleaning" the IAC does not always work, worn out internal parts driven by a high frequency PWM signal from the PCM.
replace, they wear out internally.
Clean the throttle body plate area with carb cleaner, wipe with a clean rag soaked in carb cleaner as far as you can reach in. They build up with dust and hair ***** that the AF does not catch. Jams the plate from closure until vacuum builds up behind plate.
Check for codes, not all pop at CEL.
replace, they wear out internally.
Clean the throttle body plate area with carb cleaner, wipe with a clean rag soaked in carb cleaner as far as you can reach in. They build up with dust and hair ***** that the AF does not catch. Jams the plate from closure until vacuum builds up behind plate.
Check for codes, not all pop at CEL.
Lead Driver
Joined: Sep 2003
Posts: 7,018
Likes: 210
From: SoCal
My "favorite" cause is a loose vacuum line; check to make sure all the lines and plugs on the tree at the rear of the intake manifold, driver's side, are in place.
You can test the air bypass valve by unplugging it while it's in this high idle mode and see if it drops. If so, the valve is working, but the EEC is opening it up for some reason. Then it's a sensor problem; there are sensors for temperature, oxygen, and throttle position.
Air flowing through the MAF sensor comes directly from the filter, so should remain relatively clean, unless the paper filter element is disintegrating. The throttle plate builds up oily residue from the PCV, which enters the air tube behind the MAF sensor. Later models also have EGR, which puts more crud into the intake tract, behind the throttle plate. Sometimes you have to use a stiff wire brush and carb cleaner to loosen that stuff up.
You can test the air bypass valve by unplugging it while it's in this high idle mode and see if it drops. If so, the valve is working, but the EEC is opening it up for some reason. Then it's a sensor problem; there are sensors for temperature, oxygen, and throttle position.
Air flowing through the MAF sensor comes directly from the filter, so should remain relatively clean, unless the paper filter element is disintegrating. The throttle plate builds up oily residue from the PCV, which enters the air tube behind the MAF sensor. Later models also have EGR, which puts more crud into the intake tract, behind the throttle plate. Sometimes you have to use a stiff wire brush and carb cleaner to loosen that stuff up.
Thread Starter
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Mountain Pass
Joined: Oct 2002
Posts: 206
Likes: 0
From: Jaqcksonville
My "favorite" cause is a loose vacuum line; check to make sure all the lines and plugs on the tree at the rear of the intake manifold, driver's side, are in place.
You can test the air bypass valve by unplugging it while it's in this high idle mode and see if it drops. If so, the valve is working, but the EEC is opening it up for some reason. Then it's a sensor problem; there are sensors for temperature, oxygen, and throttle position.
Air flowing through the MAF sensor comes directly from the filter, so should remain relatively clean, unless the paper filter element is disintegrating. The throttle plate builds up oily residue from the PCV, which enters the air tube behind the MAF sensor. Later models also have EGR, which puts more crud into the intake tract, behind the throttle plate. Sometimes you have to use a stiff wire brush and carb cleaner to loosen that stuff up.
You can test the air bypass valve by unplugging it while it's in this high idle mode and see if it drops. If so, the valve is working, but the EEC is opening it up for some reason. Then it's a sensor problem; there are sensors for temperature, oxygen, and throttle position.
Air flowing through the MAF sensor comes directly from the filter, so should remain relatively clean, unless the paper filter element is disintegrating. The throttle plate builds up oily residue from the PCV, which enters the air tube behind the MAF sensor. Later models also have EGR, which puts more crud into the intake tract, behind the throttle plate. Sometimes you have to use a stiff wire brush and carb cleaner to loosen that stuff up.
Follow up. I ordered the motorcraft bypass. I guess after 426k miles it needed replacing. Installed new one and all problems high idle, idle surge have gone. Thanks for the pointers.
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