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Abnormal idle

Old 10-18-2018, 05:19 PM
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Default Abnormal idle

Hello all,

I have a 94 f150 with the 5.8 that is just off a bit when idling. It almost feels like it is idling just a hair low at times, not all the time. I did recently change the ecu, but it was there before. I did find a hole in egr tube and replaced that, but the new one has me concerned, is there supposed to be play where it attached to the exhaust? Theres not a lot of play but its definitely there when I try to move it. I changed plugs, wires, cap/rotor, and air filter, no help. Showing no codes, unplugged iac and it idled like garbage and stalled, i dont believe it's that. The thing is screaming vaccuum leak, but I dont see one, other than the play in egr tube. Is there anything else I should check before I change out all the vacuum lines? Thanks for any help you guys can give.
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Old 10-19-2018, 12:42 PM
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"...just a bit off..." is too vague for us to help you with. There is no set idle RPM, so there's no such thing as "just a hair low". Click these & read the captions:


(phone app link)



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The EGR tube should not be loose. Is the tube loose in the fittings, or are the fittings loose in the manifold? When you had it apart, did you clean the threads & flare, and apply anti-seize lube?


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A vacuum leak would cause a HIGH idle; not low. And there is no vacuum at the EGR tube. No, you should not start throwing part$ at it, or ripping things out of the engine to replace - you'll likely just make things worse. This is the best way to check for vacuum & exhaust leaks, and most other engine noises:


(phone app link)
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Old 10-19-2018, 09:34 PM
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Wow, thanks for all the info, unfortunately my truck does not have a tach, but all I know is most of the time it idles like it always has with hiccups. Only way I can describe it. I tried tightening the egr tube more tonight, on the diagram where #3 meets #12, feels like the threads ended too soon on the manifold connection #12, and the tube nut is hitting the flare before its tight. Getting a new one in the am. And yes I cleaned and put antiseize on first. I can see buildup on the lower bend of the tube today, there is definitely a leak there, hoping this is the fix. Would that cause the idle stumble?
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Old 10-19-2018, 10:25 PM
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i'm thinking it might have a miss in it. check all the spark plugs to make sure the are functioning right.



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Old 10-19-2018, 10:37 PM
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Originally Posted by DarrinT04 View Post
i'm thinking it might have a miss in it. check all the spark plugs to make sure the are functioning right.



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man. I just knew that was gonna come up, I dont want to haha. But, i have wondered. I'll pull them tomorrow and check them too.
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Old 10-19-2018, 10:49 PM
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Originally Posted by Sean Moes View Post
...there is definitely a leak there, hoping this is the fix. Would that cause the idle stumble?
No.
Originally Posted by Sean Moes View Post
I'll pull them tomorrow and check them too.
The best thing to compare them to is the inside back cover of any Haynes manual:


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Old 10-20-2018, 12:34 PM
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here is the link for spark plugs at napa that will fit your truck. https://www.napaonline.com/en/search...=nol-veh-conds
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Old 10-20-2018, 02:33 PM
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Default Problem solved

New egr tube today, fits the way it's supposed to. No fire on #2, #3 plug gap was almost non existant, not sure why. Wires, cap and rotor replaced along with #3 plug, purrs like it should again. Btw I did recheck #3 after running and the gap is still good, that plug must have been bad out of the box and i didnt notice. Thanks for the tips guys.
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Old 10-20-2018, 03:54 PM
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i think you should test the EGR valve. you can do this by using a vacuum gauge or hand vacuum pump here are the instructions to test it. i hope this helps!
https://www.autozone.com/repairinfo/...&subtitle=test
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Old 10-20-2018, 06:35 PM
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Originally Posted by DarrinT04 View Post
i think you should test the EGR valve. you can do this by using a vacuum gauge or hand vacuum pump here are the instructions to test it. i hope this helps!
https://www.autozone.com/repairinfo/...&subtitle=test
ok, I can do that. Just curious why tho? Could the tube leak have damaged it?
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