Erattic idle/dies
Thread Starter
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Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
Erattic idle/dies
I have a 1990 f250 with a 5.8 v8 I have a new maf sensor and new throttle body and I'm in the middle of putting a egr on but the idle still goes crazy idling anywhere from 2.8k-500rpm I've checked for vacuum leaks and didn't find any. Ive replaced some hoses and connections that I thought might have a leak. Dont quite know what's wrong so if anybody has some knowledge on this it'd help a lot.
thanks
thanks
Thread Starter
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Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
can't tell if this is a serious answer but I'll try it either way. Thank you if it is.
More Turbo
Joined: Oct 2023
Posts: 607
Likes: 153
From: Canada
After reconnecting the battery, the ECU will power on and begin relearning the engine's operating parameters based on input from the new sensors. This process may take some time and driving under various conditions for the ECU to fully optimize the settings.
your block learn value might need a full reset to operate with the new sensors. This is the job of the block learn integrator. The computer in your truck is fairly sophisticated. Once all the sensors are calibrated you have to see if the condition persists. The idle air control actuator could be faulty or slow to respond. You throttle body could be worn. But if you change sensors you have to relearn the computer.
your block learn value might need a full reset to operate with the new sensors. This is the job of the block learn integrator. The computer in your truck is fairly sophisticated. Once all the sensors are calibrated you have to see if the condition persists. The idle air control actuator could be faulty or slow to respond. You throttle body could be worn. But if you change sensors you have to relearn the computer.
Thread Starter
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Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
After reconnecting the battery, the ECU will power on and begin relearning the engine's operating parameters based on input from the new sensors. This process may take some time and driving under various conditions for the ECU to fully optimize the settings.
your block learn value might need a full reset to operate with the new sensors. This is the job of the block learn integrator. The computer in your truck is fairly sophisticated. Once all the sensors are calibrated you have to see if the condition persists. The idle air control actuator could be faulty or slow to respond. You throttle body could be worn. But if you change sensors you have to relearn the computer.
your block learn value might need a full reset to operate with the new sensors. This is the job of the block learn integrator. The computer in your truck is fairly sophisticated. Once all the sensors are calibrated you have to see if the condition persists. The idle air control actuator could be faulty or slow to respond. You throttle body could be worn. But if you change sensors you have to relearn the computer.
Cargo Master
Joined: Aug 2021
Posts: 2,258
Likes: 742
From: Maryland
You probably meant to type "MAP sensor", not MAF sensor. 1990 F250's didn't have MAF sensors.
Have you pulled engine codes? Was the MAP sensor bad?
What hoses and connections did you replace?
Where did you source the throttle body? What was wrong with the old one?
Have you pulled engine codes? Was the MAP sensor bad?
What hoses and connections did you replace?
Where did you source the throttle body? What was wrong with the old one?
Thread Starter
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Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
have not pulled engine codes previous owner did and said it check engine was because of egr delete and I put that back on, I replaced the vacuum hoses near the throttle body because they were loose, previous owner sourced throttle body and I'm pretty sure the brand was bbs or bds I don't remember off the top of my head, and I replaced the map sensor because I did a quick search on the idle and that's what it gave me to be honest. I'm not to mechanicaly inclined yet and haven't had to work on an old car till now so it's new stuff
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Cargo Master
Joined: Aug 2021
Posts: 2,258
Likes: 742
From: Maryland
have not pulled engine codes previous owner did and said it check engine was because of egr delete and I put that back on, I replaced the vacuum hoses near the throttle body because they were loose, previous owner sourced throttle body and I'm pretty sure the brand was bbs or bds I don't remember off the top of my head, and I replaced the map sensor because I did a quick search on the idle and that's what it gave me to be honest. I'm not to mechanicaly inclined yet and haven't had to work on an old car till now so it's new stuff
Post pictures of your throttle body and your map sensor.
Post a few pictures of each side of your engine.
Here's a video that will give you a general idea of what the vacuum lines do, but it's not identical to your engine. The vacuum lines that aren't covered in the video are one from the vacuum tree to the MAP sensor, one to the power brake booster, and one from the PCV valve, on the passenger's side valve cover, to the upper intake.
Is the new throttle body similar to the old one?
Did you transfer the Idle Air Control Valve to the new throttle body?
Here's a picture of the Idle Air Control Valve, bolted to the side of the throttle body.
(I'll edit the picture in. It won't upload right now).
It sounds like you have a vacuum leak.
Did you use a gasket between the intake manifold and the throttle body?
The Idle Air Control Valve also needs a gasket.
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Thread Starter
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Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
Did you save the old throttle body and MAP sensor? The original parts on these trucks are generally higher quality than recently made replacement parts.
Post pictures of your throttle body and your map sensor.
Post a few pictures of each side of your engine.
Here's a video that will give you a general idea of what the vacuum lines do, but it's not identical to your engine. The vacuum lines that aren't covered in the video are one from the vacuum tree to the MAP sensor, one to the power brake booster, and one from the PCV valve, on the passenger's side valve cover, to the upper intake.
https://youtu.be/iq9mr-a5y78?si=_DNZAIOImBWkxk5O
Is the new throttle body similar to the old one?
Did you transfer the Idle Air Control Valve to the new throttle body?
Here's a picture of the Idle Air Control Valve, bolted to the side of the throttle body.
(I'll edit the picture in. It won't upload right now).
It sounds like you have a vacuum leak.
Did you use a gasket between the intake manifold and the throttle body?
The Idle Air Control Valve also needs a gasket.
Post pictures of your throttle body and your map sensor.
Post a few pictures of each side of your engine.
Here's a video that will give you a general idea of what the vacuum lines do, but it's not identical to your engine. The vacuum lines that aren't covered in the video are one from the vacuum tree to the MAP sensor, one to the power brake booster, and one from the PCV valve, on the passenger's side valve cover, to the upper intake.
https://youtu.be/iq9mr-a5y78?si=_DNZAIOImBWkxk5O
Is the new throttle body similar to the old one?
Did you transfer the Idle Air Control Valve to the new throttle body?
Here's a picture of the Idle Air Control Valve, bolted to the side of the throttle body.
(I'll edit the picture in. It won't upload right now).
It sounds like you have a vacuum leak.
Did you use a gasket between the intake manifold and the throttle body?
The Idle Air Control Valve also needs a gasket.
Thread Starter
|
Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
Did you save the old throttle body and MAP sensor? The original parts on these trucks are generally higher quality than recently made replacement parts.
Post pictures of your throttle body and your map sensor.
Post a few pictures of each side of your engine.
Here's a video that will give you a general idea of what the vacuum lines do, but it's not identical to your engine. The vacuum lines that aren't covered in the video are one from the vacuum tree to the MAP sensor, one to the power brake booster, and one from the PCV valve, on the passenger's side valve cover, to the upper intake.
https://youtu.be/iq9mr-a5y78?si=_DNZAIOImBWkxk5O
Is the new throttle body similar to the old one?
Did you transfer the Idle Air Control Valve to the new throttle body?
Here's a picture of the Idle Air Control Valve, bolted to the side of the throttle body.
(I'll edit the picture in. It won't upload right now).
It sounds like you have a vacuum leak.
Did you use a gasket between the intake manifold and the throttle body?
The Idle Air Control Valve also needs a gasket.
Post pictures of your throttle body and your map sensor.
Post a few pictures of each side of your engine.
Here's a video that will give you a general idea of what the vacuum lines do, but it's not identical to your engine. The vacuum lines that aren't covered in the video are one from the vacuum tree to the MAP sensor, one to the power brake booster, and one from the PCV valve, on the passenger's side valve cover, to the upper intake.
https://youtu.be/iq9mr-a5y78?si=_DNZAIOImBWkxk5O
Is the new throttle body similar to the old one?
Did you transfer the Idle Air Control Valve to the new throttle body?
Here's a picture of the Idle Air Control Valve, bolted to the side of the throttle body.
(I'll edit the picture in. It won't upload right now).
It sounds like you have a vacuum leak.
Did you use a gasket between the intake manifold and the throttle body?
The Idle Air Control Valve also needs a gasket.
here are those photos I'm planing on putting a egr on today but I've gotten mixed answers on whether that would help or not
Logistics Pro
Joined: Aug 2014
Posts: 3,558
Likes: 852
I'd be tempted to plug the vacuum ports on the throttle body, and the T you have there.
Then, following the BBK instructions EXACTLY, set your idle.
Have you previously followed the BBK instructions to set your idle rpm?
Why did you swap your MAP and throttle body?
If you have the exact same issue, it's obviously something else, and I'd be tempted to put the originals back on and figure out what is causing the issue.
Then, following the BBK instructions EXACTLY, set your idle.
Have you previously followed the BBK instructions to set your idle rpm?
Why did you swap your MAP and throttle body?
If you have the exact same issue, it's obviously something else, and I'd be tempted to put the originals back on and figure out what is causing the issue.
Thread Starter
|
Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
I'd be tempted to plug the vacuum ports on the throttle body, and the T you have there.
Then, following the BBK instructions EXACTLY, set your idle.
Have you previously followed the BBK instructions to set your idle rpm?
Why did you swap your MAP and throttle body?
If you have the exact same issue, it's obviously something else, and I'd be tempted to put the originals back on and figure out what is causing the issue.
Then, following the BBK instructions EXACTLY, set your idle.
Have you previously followed the BBK instructions to set your idle rpm?
Why did you swap your MAP and throttle body?
If you have the exact same issue, it's obviously something else, and I'd be tempted to put the originals back on and figure out what is causing the issue.
Thread Starter
|
Trailering
Joined: Jun 2025
Posts: 17
Likes: 2
I feel very dumb now but it worked great just doing that, funny how such a small thing creates such a big problem.
Cargo Master
Joined: Aug 2021
Posts: 2,258
Likes: 742
From: Maryland
Here's a video on various under hood components.