Contour Enthusiasts Group Archives Forums Modifications Duratec Performance rattling/popping at end of gear acceleration

... but if it's pinging you will want to use more than 87 regardless of what the manual says. Added octane will help somewhat with the pinging (if that's what the problem is)

You say this started after installing an intake? Check all your connections for leaks, which could let un-metered air in and throw off timing.