Noise inside intake at idle

[93notchback]

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)

 

[mhespenh]

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)

If it sounds like a ball-pin hammer banging on metal making a "ping" sound, that would be what it is: Pinging.

Check your timing, it is probably too advanced, or switch to a higher octane fuel (premium instead of regular).

From wikipedia:

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.