Rough Idle when Cold Help (video)
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Rough Idle when Cold Help (video)
My 78' F250 with a 400 idles roughly when cold. It has had a fresh tune up less than 3K miles ago. After 5 minutes or so it runs much smoother. Here is a video of the vacuum gauge while cold and warm. The vacuum bounces and is much lower when cold. I have checked for an intake gasket leak and found nothing. Any ideas on what to do? Thanks.
YouTube - Rough Idle
YouTube - Rough Idle
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Joined: Nov 2008
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I think you need to define the tune up, what was done that way we can give you some insight on what to check. Was this change in performance noticed right after the tune up? How long has it been doing this? Just some more info needed
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New plugs, distributor cap and rotor, wires, air filter, fuel filter.
After the tune up last year it ran perfect. The rough idle was something that started out slowly and has progressively gotten worse.
After the tune up last year it ran perfect. The rough idle was something that started out slowly and has progressively gotten worse.
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Logistics Pro
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After it warms up nothing much. Runs good. Just very rough idle and stumbling when first started.
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Post Fiend
Joined: Apr 2008
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From: Big Sky Country
It's possible to have a vacuum leak present on a cold motor that "goes away" as the motor reaches operating temp, your gauge indicates a shaky 17" at cold start-up and a relatively steady 22" after warm-up so it's a strong possibility that's your issue.
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Logistics Pro
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Is there a device that that draws vacuum that could close or seal up when warm?
FTE Emeritus
Joined: Jan 2006
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From: springfield Missouri area
Sounds like your choke pull off is not opening the choke far enough to run smooth. Start when cold and look at choke plate and see if it opens @ 1/4 inch. If it is not opening very far , take your finger and open it a little and see if engine smooths out.
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Logistics Pro
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I will check this out.
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Logistics Pro
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Well fixed a few vacuum leaks-bad diaphragm on choke pull off, loose vacuum tree- and the truck runs much better. It now idles much lower than before. Would a vacuum leak cause the engine to idle higher than normal?