2 Valve V10, idle is too fast
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2 Valve V10, idle is too fast
I have owned my '02 F250 for about 3 months and over that time the idle has become progressively faster. Its a manual transmission so it doesn't cause as much trouble as it would in an auto but this is annoying and compression braking suffers. I did some searching on the forum and found that dirty IAC valves are a common problem. I removed mine and found it to be pretty nasty with carbon and sticking. I cleaned it up and got it to stop sticking but the springs still don't push the valve fully closed. I assume that the springs are supposed to keep the valve closed and the PCM commands the coil to pull the valve open against the spring. So I reinstalled the clean valve but the idle is still pretty fast. Before anyone suggest other vacuum leaks, I pinched the supply hose to the IAC valve and that drives the idle down to a near stall.
My two questions:
Should the spring force the IAC valve fully closed?
Does the PCM take some time to learn a new idle after the valve is cleaned or replaced?
A new IAC valve is pretty cheap but I don't want to buy one if there is another problem I am overlooking.
Thanks,
My two questions:
Should the spring force the IAC valve fully closed?
Does the PCM take some time to learn a new idle after the valve is cleaned or replaced?
A new IAC valve is pretty cheap but I don't want to buy one if there is another problem I am overlooking.
Thanks,
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New User
Joined: Feb 2011
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I cleaned the throttle body as jh suggested. It wasn't too dirty and was not the cause. I replaced the IAC valve and that seems to have taken care of the problem. Idle is down to about 750RPM when the engine is warm. Before I changed the valve it was idling between 1500 and 1700 RPM.
For future troubleshooting it might be worth knowing that the IAC valve is held full open by the springs. This means that if the coil or wiring failed the engine would idle very fast. The PCM energizes the coil to pull the valve closed. A good valve travels very smooth and makes a hissing noise when you operate it manually. It must have some sort of pneumatic damper in it.
If the valve doesn't travel smoothly when operated by hand and doesn't stand full open by the springs, its got problems. Some people have said that cleaning the valve solved their problem but I guess mine was too far gone.
For future troubleshooting it might be worth knowing that the IAC valve is held full open by the springs. This means that if the coil or wiring failed the engine would idle very fast. The PCM energizes the coil to pull the valve closed. A good valve travels very smooth and makes a hissing noise when you operate it manually. It must have some sort of pneumatic damper in it.
If the valve doesn't travel smoothly when operated by hand and doesn't stand full open by the springs, its got problems. Some people have said that cleaning the valve solved their problem but I guess mine was too far gone.
Logistics Pro
Joined: Aug 2007
Posts: 3,974
Likes: 15
From: Millersburg, OH
I cleaned the throttle body as jh suggested. It wasn't too dirty and was not the cause. I replaced the IAC valve and that seems to have taken care of the problem. Idle is down to about 750RPM when the engine is warm. Before I changed the valve it was idling between 1500 and 1700 RPM.
For future troubleshooting it might be worth knowing that the IAC valve is held full open by the springs. This means that if the coil or wiring failed the engine would idle very fast. The PCM energizes the coil to pull the valve closed. A good valve travels very smooth and makes a hissing noise when you operate it manually. It must have some sort of pneumatic damper in it.
If the valve doesn't travel smoothly when operated by hand and doesn't stand full open by the springs, its got problems. Some people have said that cleaning the valve solved their problem but I guess mine was too far gone.
For future troubleshooting it might be worth knowing that the IAC valve is held full open by the springs. This means that if the coil or wiring failed the engine would idle very fast. The PCM energizes the coil to pull the valve closed. A good valve travels very smooth and makes a hissing noise when you operate it manually. It must have some sort of pneumatic damper in it.
If the valve doesn't travel smoothly when operated by hand and doesn't stand full open by the springs, its got problems. Some people have said that cleaning the valve solved their problem but I guess mine was too far gone.
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New User
Joined: Feb 2011
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I will take a look at the MAF and see if it looks dirty. What sort of cleaner is recommended?
SKI, I was not aware that disconnecting the battery would clear the stored fuel trims. I will try this as well. I'm interested to see what sort of mileage I will get with this truck. Its not my daily driver we bought it to pull the boat.
SKI, I was not aware that disconnecting the battery would clear the stored fuel trims. I will try this as well. I'm interested to see what sort of mileage I will get with this truck. Its not my daily driver we bought it to pull the boat.
Cargo Master
Joined: Jul 2009
Posts: 2,885
Likes: 24
From: Chino, California
I used CRC MAF cleaner. You can get it at your chain auto parts stores. Comes in a spray can for about $6.
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