rough idle

#1
1997 1.6L: at around 70,000 miles, suddenly began idling very rough which smooths out as rpms increase. has 100,000 now. did all of the recommended smog and ignition component replacements, replaced all four engine mounts. Suspecting a cam ware or valve spring issues. A burn’t valve would have gotten worse by now. Does anyone else have a similar problem?
 
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