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- - Idle Issue (https://67-72chevytrucks.com/vboard/showthread.php?t=775126)

Classics Fan

11-13-2018 01:49 PM

Idle Issue

My 1971 Jimmy with the original 350 has recently developed a problem at idle. It runs fine for a minute or so then slowly begins to decrease to the point of running rough and threatens to die without feathering the throttle. When I do that it has some initial hesitation as well. The problem seems to have developed suddenly, not progressively. It runs fine down the road, no lack of power or ignition miss. Any thoughts or ideas on what could be causing the idle issue? TIA!
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SeventyOne

11-13-2018 01:58 PM

Re: Idle Issue

Whats your idle RPM?

Could be a vacuum leak.

lks dcvn

11-13-2018 02:44 PM

Re: Idle Issue

:agree:

geezer#99

11-13-2018 03:07 PM

Re: Idle Issue

It’s the weather!
Cooler moist air is the problem.
It creates a colder intake.
Cold fuel vapour inside the intake reverts back to a liquid. The liquid gas puddles in the intake. Some vapour gets to the chamber but is too lean to support god combustion. It runs rough.
Cure is a heat soak. Usually when it starts to run rough if you shut it off for 5 minutes and wait for the hot air in the lifter valley to heat the intake then you’ll be good to go.

Classics Fan

11-13-2018 04:32 PM

Quote:

Originally Posted by SeventyOne (Post 8383500)

Whats your idle RPM?

Could be a vacuum leak.

No tach. My best guess is around 800 RPM in park and 500-600 in drive. Vacuum hoses are in good condition but I will double-check the connections. Thanks for the suggestion.
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Classics Fan

11-13-2018 04:35 PM

Quote:

Originally Posted by geezer#99 (Post 8383557)

The problem persists regardless of ambient and/or engine temps.
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SeventyOne

11-13-2018 05:07 PM

Re: Idle Issue

Quote:

Originally Posted by Classics Fan (Post 8383610)

Next i'd inspect/replace the plugs.

geezer#99

11-13-2018 06:39 PM

Re: Idle Issue

Quote:

Originally Posted by Classics Fan (Post 8383613)

The problem persists regardless of ambient and/or engine temps.
Posted via Mobile Device

Ah!
So it happens all the time, not just when you start it cold.
That makes it easier!
I think I know what it is!

Classics Fan

11-13-2018 07:15 PM

Quote:

Originally Posted by geezer#99 (Post 8383686)

Ah!
So it happens all the time, not just when you start it cold.
That makes it easier!
I think I know what it is!

I think the problem is solved, pending a test drive in a few minutes. I’m still interested in hearing your thoughts.
Posted via Mobile Device

Classics Fan

11-13-2018 08:37 PM

Quote:

Originally Posted by SeventyOne (Post 8383500)

Whats your idle RPM?

Could be a vacuum leak.

Mad remote troubleshooting and diagnosis, SeventyOne! I found the vacuum line to the PVC valve disconnected at a tee. Reconnected and it runs like new again! Thanks, and I appreciate everyone’s input! Hope to repay with some good advice of my own to someone in need in the future.
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SeventyOne

11-13-2018 08:41 PM

Re: Idle Issue

Awesome glad it was a cheap and easy fix!

lks dcvn

11-14-2018 02:54 PM

Re: Idle Issue

:metal:

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