360 fe fluctuating idle
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Junior User
Joined: Mar 2017
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From: Tualatin OR
360 fe fluctuating idle
the 360 fe in my 73 f250 has a constantly fluctuating idle it reminds me of a vacuum leak. idk if there's a hose that's supposed to be attached here but this is the only thing i can find that looks like its missing a hose idk what it is any info would be greatly appreciated
Logistics Pro
Joined: Jul 2005
Posts: 4,217
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That is a Temperature Controlled Vacuum Switch. It's OK sitting there, as it has no vacuum source to leak. It sources vacuum from the manifold and then routes it to an accessory, based on engine/coolant temperature.
You can check your vacuum advance on the distributor for leaking.
And if your carburetor has an electric choke, make sure it's connected. OEM Autolite/Motorcraft get AC voltage from the Stator lug on the alternator, while aftermarket carbs/chokes tend to use normal 12V+ DC power.
You can check your vacuum advance on the distributor for leaking.
And if your carburetor has an electric choke, make sure it's connected. OEM Autolite/Motorcraft get AC voltage from the Stator lug on the alternator, while aftermarket carbs/chokes tend to use normal 12V+ DC power.
Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
Sometimes a worn throttle shaft can cause the problems you describe. Exsessive clearance in the throttle shaft can cause a vacuum leak
With the engine off, disconnect the throttle linkage and the throttle return springs. Grab the throttle linkage and move it front to back and then up and down.
If you have much more front to back play than you do up and down there is a good chance that is your problem. Not real scientific, but it is a good check.
Good luck.
With the engine off, disconnect the throttle linkage and the throttle return springs. Grab the throttle linkage and move it front to back and then up and down.
If you have much more front to back play than you do up and down there is a good chance that is your problem. Not real scientific, but it is a good check.
Good luck.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
When does this occur, initial start-up (Cold)?, Warm Idle?
What is the RPM fluctuation range?
What is the Vacuum fluctuation range?
What is the RPM fluctuation range?
What is the Vacuum fluctuation range?
Last edited by vjsimone; Jul 1, 2017 at 08:46 AM. Reason: Adding Text
Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
The rpm fluctuation and vacuum fluctuations are directly related to the amount of wear in the throttle shaft bores. The more wear, the more fluctuations.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
More noticeable when the engine is warmed up, at operating temperature and at idle. When first started the choke operation can tend to mask the problem.
The rpm fluctuation and vacuum fluctuations are directly related to the amount of wear in the throttle shaft bores. The more wear, the more fluctuations.
The rpm fluctuation and vacuum fluctuations are directly related to the amount of wear in the throttle shaft bores. The more wear, the more fluctuations.
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Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
the 360 fe in my 73 f250 has a constantly fluctuating idle it reminds me of a vacuum leak. idk if there's a hose that's supposed to be attached here but this is the only thing i can find that looks like its missing a hose idk what it is any info would be greatly appreciated
What is the RPM fluctuation range?
What is the Vacuum fluctuation range?
There were hoses attached to that "Temperature Controlled Vacuum Switch", all that plumbing disappears over time, mostly because no time is invested in understanding what it does.
You should check around to see if you have any unconnected hose, if you do, hopefully they are plugged. Better to remove stray hoses, and cap off unless your in re-creation mode.
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Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
[QUOTE=vjsimone;17298541]
There were hoses attached to that "Temperature Controlled Vacuum Switch", all that plumbing disappears over time, mostly because no time is invested in understanding what it does.
QUOTE]
A lot of truth in that statement!
There were hoses attached to that "Temperature Controlled Vacuum Switch", all that plumbing disappears over time, mostly because no time is invested in understanding what it does.
QUOTE]
A lot of truth in that statement!
Thread Starter
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Junior User
Joined: Mar 2017
Posts: 52
Likes: 0
From: Tualatin OR
When does this occur, initial start-up (Cold)?, Warm Idle?
What is the RPM fluctuation range?
What is the Vacuum fluctuation range?
There were hoses attached to that "Temperature Controlled Vacuum Switch", all that plumbing disappears over time, mostly because no time is invested in understanding what it does.
You should check around to see if you have any unconnected hose, if you do, hopefully they are plugged. Better to remove stray hoses, and cap off unless your in re-creation mode.
What is the RPM fluctuation range?
What is the Vacuum fluctuation range?
There were hoses attached to that "Temperature Controlled Vacuum Switch", all that plumbing disappears over time, mostly because no time is invested in understanding what it does.
You should check around to see if you have any unconnected hose, if you do, hopefully they are plugged. Better to remove stray hoses, and cap off unless your in re-creation mode.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
More noticeable when the engine is warmed up, at operating temperature and at idle. When first started the choke operation can tend to mask the problem.
The rpm fluctuation and vacuum fluctuations are directly related to the amount of wear in the throttle shaft bores. The more wear, the more fluctuations.
The rpm fluctuation and vacuum fluctuations are directly related to the amount of wear in the throttle shaft bores. The more wear, the more fluctuations.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
it happens when warm for example when im at a stop light. idk if it happens when cold i hold it at around 1200 rpm (estimate i dont have a tach) when i first start it because well cold blooded. the auto choke doesnt seem to like to keep it running when cold... but yeah even when warm she likes to fluctuate about (by ear) 200-500 rpm again idk i dont have a tach
You may be due for a Carb rebuild, you can check out the mechanical parts that Rodger & MeanGreen discus as well. Those throttle shafts are an issue sometimes in the EFI/Throttle Body as well.
Good time to fix/adjust the choke as well.
What Carb do you have?
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Junior User
Joined: Mar 2017
Posts: 52
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From: Tualatin OR
I'm with the other lads on Carb issues. 85% of fluctuations are usually Carb related, and additionally Fuel related, including fuel filter clogging, fuel pump diaphragm failing, and air leaks.
You may be due for a Carb rebuild, you can check out the mechanical parts that Rodger & MeanGreen discus as well. Those throttle shafts are an issue sometimes in the EFI/Throttle Body as well.
Good time to fix/adjust the choke as well.
What Carb do you have?
You may be due for a Carb rebuild, you can check out the mechanical parts that Rodger & MeanGreen discus as well. Those throttle shafts are an issue sometimes in the EFI/Throttle Body as well.
Good time to fix/adjust the choke as well.
What Carb do you have?
Logistics Pro
Joined: Jul 2005
Posts: 4,217
Likes: 154
From the more amateur bag of tricks, you can try disconnecting vacuum lines, all at once or one at a time, and seeing if it's an intermittent leak away from the engine.
But my suspicions still lie with the fast idle system.
If I remember correctly from my young and dumb days, the rationale was if I didn't know what the part was, or understand its function, I didn't need it on there...
...a classic example being the the hot air tube from the exhaust manifold to the choke housing, and the wire for the electric choke heater, on my old '82 Mustang GT's 2150. That car always had a rolling inconsistant idle before I put a four barrel setup on it...
Without needed heat channels to the choke, it will react instead to the ambient temperatures under the hood, which could be enough to make a noticeable difference.
But my suspicions still lie with the fast idle system.
...a classic example being the the hot air tube from the exhaust manifold to the choke housing, and the wire for the electric choke heater, on my old '82 Mustang GT's 2150. That car always had a rolling inconsistant idle before I put a four barrel setup on it...Without needed heat channels to the choke, it will react instead to the ambient temperatures under the hood, which could be enough to make a noticeable difference.
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