f150 idle issues
Thread Starter
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New User
Joined: Jan 2014
Posts: 9
Likes: 0
From: New Castle, Indiana
f150 idle issues
hello all
My 1997 f150 5.4 has started an idle issue.
The truck when started will idle around1200 rpm and not settle down
After driving a bit it will drop down around 800 and idle rough and sounds like it has a plug fouled. As soon as you give it gas it clears up and sounds fine, then drops down an idles rough.
Checked for vacuum leaks but don't see any. pulled the MAP sensor and cleaned it, but did not change.
Any input
thanks
Larry
My 1997 f150 5.4 has started an idle issue.
The truck when started will idle around1200 rpm and not settle down
After driving a bit it will drop down around 800 and idle rough and sounds like it has a plug fouled. As soon as you give it gas it clears up and sounds fine, then drops down an idles rough.
Checked for vacuum leaks but don't see any. pulled the MAP sensor and cleaned it, but did not change.
Any input
thanks
Larry
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Remove the Intake Air Controller (IAC) and spray clean it inside
Make sure the Pintel valve inside is free to move.
Remove the large intake hose from the throttle body and spray clean the inside until it runs out clean.
The cleaner is available at a auto parts store.
Good luck.
Make sure the Pintel valve inside is free to move.
Remove the large intake hose from the throttle body and spray clean the inside until it runs out clean.
The cleaner is available at a auto parts store.
Good luck.
Thread Starter
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New User
Joined: Jan 2014
Posts: 9
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From: New Castle, Indiana
hello
after cleaning everything the problem still is there. code shows po171 and po174. what is strange is as soon as you touch the throttle it runs fine. Don't know if a bad oxygen sensor would do this or not. It acts like an old school vacuum leak off of the intake use to do. I sprayed all around and got no reaction.
thanks
after cleaning everything the problem still is there. code shows po171 and po174. what is strange is as soon as you touch the throttle it runs fine. Don't know if a bad oxygen sensor would do this or not. It acts like an old school vacuum leak off of the intake use to do. I sprayed all around and got no reaction.
thanks
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
You did not mention codes in your first post.
Those codes indicate an air leak into the intake tract.
Most likely the rubber part on the rear of the upright intake manifold has gone open to air.
This causes the fuel tables to shift 'rich' trying to correct for excess air and sets codes for both banks since the issue is common to both banks..
With this condition the idle and low speed drivability will be poor after a cold motor heats to running temperature..
At highway speed the motor will appear to run normal but get rough or stall at idle.
Repair for an air leak. Leave the OX sensors alone. They are not the cause.
Good luck.
Those codes indicate an air leak into the intake tract.
Most likely the rubber part on the rear of the upright intake manifold has gone open to air.
This causes the fuel tables to shift 'rich' trying to correct for excess air and sets codes for both banks since the issue is common to both banks..
With this condition the idle and low speed drivability will be poor after a cold motor heats to running temperature..
At highway speed the motor will appear to run normal but get rough or stall at idle.
Repair for an air leak. Leave the OX sensors alone. They are not the cause.
Good luck.
Thread Starter
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New User
Joined: Jan 2014
Posts: 9
Likes: 0
From: New Castle, Indiana
hello
Still working on these issues.
replaced all vacuum lines
pulled and cleaned the idle air valve
tapped on valve with a hammer no response
sprayed all areas and no response.
Really don't know if the idle valve is working.
does anyone know if you can bench check the valve, not sure what voltage
is sent to it.
no change in the condition.
Thanks
Still working on these issues.
replaced all vacuum lines
pulled and cleaned the idle air valve
tapped on valve with a hammer no response
sprayed all areas and no response.
Really don't know if the idle valve is working.
does anyone know if you can bench check the valve, not sure what voltage
is sent to it.
no change in the condition.
Thanks
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
IAC test.
Normal hot idle is 650 +/-50 rpm as monitored by the computer.
Simply to test the IAC at hot idle, remove it's connector.
The idle should drop to about 500 +/- if the IAC is functioning at all.
If the idle is affected by the fault, the test may not be so accurate until the air leak is found and repaired.
The codes absolutely indicate an air leak.
The codes indicate the fuel tables have shifted lean.
This will affect idle and cause stalling and rough idle on a fully hot motor.
Spray methods of finding a leak is not fool proof if a combustable spray is not used and does not get to the area of the leak.
Non combustible spray cleaner will not work.
.
Did you check out the PCV hose connection on the rear of the
'vertical' intake manifold?
This is the fault most often causing the rough idle and stalling. The rubber fitting goes soft with intake vacuum sucking a hole in the soft rubber caused by the crank case fumes.
.
If a Scanner is used to monitor the fuel tables when a combustible spray enters the leak area, the table values change near instantly due to the OX sensors immediate reactions sending their signals back to the computer.
Good luck..
Normal hot idle is 650 +/-50 rpm as monitored by the computer.
Simply to test the IAC at hot idle, remove it's connector.
The idle should drop to about 500 +/- if the IAC is functioning at all.
If the idle is affected by the fault, the test may not be so accurate until the air leak is found and repaired.
The codes absolutely indicate an air leak.
The codes indicate the fuel tables have shifted lean.
This will affect idle and cause stalling and rough idle on a fully hot motor.
Spray methods of finding a leak is not fool proof if a combustable spray is not used and does not get to the area of the leak.
Non combustible spray cleaner will not work.
.
Did you check out the PCV hose connection on the rear of the
'vertical' intake manifold?
This is the fault most often causing the rough idle and stalling. The rubber fitting goes soft with intake vacuum sucking a hole in the soft rubber caused by the crank case fumes.
.
If a Scanner is used to monitor the fuel tables when a combustible spray enters the leak area, the table values change near instantly due to the OX sensors immediate reactions sending their signals back to the computer.
Good luck..
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Thread Starter
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New User
Joined: Jan 2014
Posts: 9
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From: New Castle, Indiana
hello all
problems have been put to rest.
Replaced all vacuum lines and also the IAP valve.
Runs fine
Thanks for all the help and info
Larry
problems have been put to rest.
Replaced all vacuum lines and also the IAP valve.
Runs fine
Thanks for all the help and info
Larry
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