What causes 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, 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.

I think with all the threads you have on this thing it is just worn out. Might be time to update to a newer Mustang.

I don’t know what you mean by “valve chatter”, you’re probably hearing knocking/pre-ignition. Nothing with valve adjustment would be affected by different octane gas. But why the new thread?

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@Austin_Travis
Including this thread, You have 4 different threads for this same problem.

Your chances of getting help go down with each thread you start.

If changing fuel octane made the problem go away, it’s not valve clatter, it’s ignition timing.




I apologize for posting multiple times but the main reason for this thread is that I have incorrect assumptions in the past ones, as it seems I still do, and this time I was asking a more general question because I have resolved other issues in the past ones threads and wanted to take other factors out do the equation. Clearly I do not know much about timing and I am trying to fix it and figure it out myself. Also, I did not know that once a thread is posted that it doesn’t just move away and disappear after a few days.