Causes of valve chatter.
I have a 2004 3.9l v6 Mustang with 125k miles and the valves started chattering with 87 octane a few months ago so I just started running 93 octane and now they’re starting to chatter with 93 octane. The chattering doesn’t appear until driving for after about 30 minutes. The chattering starts with a very light load on the engine and then disappears after about 3500 rpm. It is the loudest when accelerating around 2500 rpms and at highway speeds with even the lightest touch to the throttle. I have new spark plugs, no slack in timing chain, there are no exhaust leaks, good egr, and the imrc actuator rods are connected. Does anyone know what could be the cause of the valves chattering? And would torquing the rockers possibly have any effect? Thanks.