Noise inside intake at idle

93notchback said:

Got a 95 gt that has a loud thumping noise inside the intake when idling. Sounds like a backfire inside the intake( you can feel it with your hand). Car runs a little rough, goes away somewhat when the rpms. Possible timing or lean condition?? Thanks for any help. Going to pull the codes in the morning (no check engine light)

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Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

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