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Old 11-15-2002, 03:41 PM
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Post Pontiac 400 idles rough when hot

When my firebird 400 is fully warmed up, it runs rough at low rpms and threatens to stall when idling. It runs and idles fine when cold, and also runs well at freeway speeds when hot. Any suggestions?

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Old 12-15-2003, 11:35 AM
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what kind of carb do you have
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Old 12-15-2003, 01:31 PM
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Sounds like an intake leak. When cold, the choke is over richening the mixture and can cover up a vacuum leak. At higher speeds vacuum leaks can go un-noticed.

On the older Pontiac intake gaskets, they used a steel center with paper on both sides. I"ve changed lots of them in my day. The paper sides shrink down and get sucked into the manifold, leaving a small intake leak on each affected runner. Try spraying some carb cleaner where each intake runner meets the heads and see if you find where its leaking. Could also be a vacuum hose or carb base gasket too.
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