High idle only while using AC
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Joined: Oct 2005
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From: MICHIGAN
High idle only while using AC
01’ Screw 5.4. Anyone ever experience a high idle only when the AC is on? Idles and runs perfect when ac is off. It recently just started doing this so I replaced the IAC with a motorcraft unit with no change. In gear with ac on it will run up to 35mph without even touching the throttle. I’ve been just turning it off when coming up to stop lights. Where should I look? Is the TPS capable of this?
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From: MICHIGAN
Fleet Mechanic
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From: WA
You could unplug the IAC valve while the idle is high and see if idle RPM drop. If it does that would be a sign of the PCM commanding it high for some reason. If it doesn't that might be a sign of something else stuck, letting more air in.
Might not be conclusive but it might at least take the main idle speed control component, the IACV, out of the picture. If the PCM is opening the IACV that would be a different path to follow than the TPS, I think.
If it only happens in gear I'd guess that you'll have to use the parking brake or chock the wheels or lift the back wheels to do that. Good luck.
Might not be conclusive but it might at least take the main idle speed control component, the IACV, out of the picture. If the PCM is opening the IACV that would be a different path to follow than the TPS, I think.
If it only happens in gear I'd guess that you'll have to use the parking brake or chock the wheels or lift the back wheels to do that. Good luck.
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From: MICHIGAN
This was my first thought also so I replaced it with a motorcraft and no change. I’ll check for vacuum leaks next.
Fleet Mechanic
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From: WA
Or are you saying that it can stay in drive, as long as you're stopped, before it drops? The clues aren't really clear.
Any chance your foot is on the brake pedal when the idle speed goes up? Could be a bad brake booster. Some people put their foot on the brake pedal right as they shift to Drive. Easy to check.
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Joined: Oct 2005
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From: MICHIGAN
Good luck. Could be a day of twenty second inspections and putting it in Drive. That seems to be what you're saying - put it in drive, idle speed rises, put it in park, idle speed drops.
Or are you saying that it can stay in drive, as long as you're stopped, before it drops? The clues aren't really clear.
Any chance your foot is on the brake pedal when the idle speed goes up? Could be a bad brake booster. Some people put their foot on the brake pedal right as they shift to Drive. Easy to check.
Or are you saying that it can stay in drive, as long as you're stopped, before it drops? The clues aren't really clear.
Any chance your foot is on the brake pedal when the idle speed goes up? Could be a bad brake booster. Some people put their foot on the brake pedal right as they shift to Drive. Easy to check.
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Fleet Mechanic
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From: WA
I think that 01 uses an electrically controlled vacuum actuator for some of the flow control doors in the system. Not the blend door but one or more of the defrost or floor/panel controls, or fresh air versus cabin air. Like Max AC uses only cabin air. Might be worth checking those. Maybe it is a leak caused when the valve is actuated.
Check if the problem happens on all of the settingsthat used cooled air or only some of them. Might be a clue. Maybe a leaking vacuum hose after the actuator. Don't really know the details even though I have the same system.
Edited - the problem might just be coincidental to AC. Many of the other settings also use the AC compressor. I have the Shop Manual that tells which doors have full vacuum and which don't for each setting, if you come back with more clues. Good luck.
Check if the problem happens on all of the settings
Edited - the problem might just be coincidental to AC. Many of the other settings also use the AC compressor. I have the Shop Manual that tells which doors have full vacuum and which don't for each setting, if you come back with more clues. Good luck.
Hotshot
Joined: Jul 2020
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From: Near Salt Lake City
Could be a frayed throttle cable too
Check the fuel trims to see if it's a vacuum leak or not
Check the TP PID back and forth as you move the throttle
Should start out around .8 volts at closed throttle and go up to around 4.5 volts at WOT
Check the fuel trims to see if it's a vacuum leak or not
Check the TP PID back and forth as you move the throttle
Should start out around .8 volts at closed throttle and go up to around 4.5 volts at WOT
Thread Starter
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More Turbo
Joined: Oct 2005
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From: MICHIGAN
I think that 01 uses an electrically controlled vacuum actuator for some of the flow control doors in the system. Not the blend door but one or more of the defrost or floor/panel controls, or fresh air versus cabin air. Like Max AC uses only cabin air. Might be worth checking those. Maybe it is a leak caused when the valve is actuated.
Check if the problem happens on all of the settingsthat used cooled air or only some of them. Might be a clue. Maybe a leaking vacuum hose after the actuator. Don't really know the details even though I have the same system.
Edited - the problem might just be coincidental to AC. Many of the other settings also use the AC compressor. I have the Shop Manual that tells which doors have full vacuum and which don't for each setting, if you come back with more clues. Good luck.
Check if the problem happens on all of the settings
Edited - the problem might just be coincidental to AC. Many of the other settings also use the AC compressor. I have the Shop Manual that tells which doors have full vacuum and which don't for each setting, if you come back with more clues. Good luck.
Fleet Mechanic
Joined: Jun 2023
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From: WA
The only difference between AC and Panel, for 2003, is that the AC compressor does not operate. The two vacuum motors experience the same vacuum settings.
And the AC compressor does operate for other settings besides Max AC, AC, and Defrost. Like Panel/Floor and Floor/Defrost.
So there's no obvious common element for the settings with the problem. Stumped.
And the AC compressor does operate for other settings besides Max AC, AC, and Defrost. Like Panel/Floor and Floor/Defrost.
So there's no obvious common element for the settings with the problem. Stumped.
Fleet Mechanic
Joined: Jun 2023
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From: WA
I'd still try disconnecting the IACV. Break the problem down in to parts, vacuum leak or PCM control or sticking throttle cable. You could also plug the vacuum line at the vacuum bottle to see if it's a vacuum leak through the controls. Take the snow shield off of the throttle bell crank and force it closed by hand. That's three separate possible reasons for a high idle.
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More Turbo
Joined: Oct 2005
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From: MICHIGAN
I'd still try disconnecting the IACV. Break the problem down in to parts, vacuum leak or PCM control or sticking throttle cable. You could also plug the vacuum line at the vacuum bottle to see if it's a vacuum leak through the controls. Take the snow shield off of the throttle bell crank and force it closed by hand. That's three separate possible reasons for a high idle.
Thread Starter
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More Turbo
Joined: Oct 2005
Posts: 560
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From: MICHIGAN
I'd still try disconnecting the IACV. Break the problem down in to parts, vacuum leak or PCM control or sticking throttle cable. You could also plug the vacuum line at the vacuum bottle to see if it's a vacuum leak through the controls. Take the snow shield off of the throttle bell crank and force it closed by hand. That's three separate possible reasons for a high idle.