Your DEC may be too perfectly balanced, and your polar alignment may be too good.

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Seems contradictory but if there is any backlash in your DEC then every time you correct (say) a negative DEC error you may overcompensate.

Then you have a positive error, which it then also overcompensates. The cycle continues then, which it looks like what is happening.

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One thing to try is to reduce the DEC aggressiveness (aka feedback). That may, just may, fix it. I say that because your graph makes it appear your

DEC corrections are overshooting on a periodic basis. PEC is a non-issue with DEC as DEC guiding commands will rarely, if ever, cause a worm cycle.

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Another thing to try is to turn off Auto DEC and force it to correct in only one direction - namely that needed to correct any (tiny, but not too tiny) DEC drift.

That way it will never reverse so, with a tiny amount of DEC imbalance (in the right direction) the DEC gear will always be engaged.

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Same idea as RA being heavy east and guiding aggressiveness in the range of 0.5X. Doing that guarantees it will never reverse so any backlash is a non-issue.

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You will need, of course, to figure out which (if any) direction you have DEC drift. But a bit of experimentation will tell you which works for any particular target.

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A tiny amount of DEC drift, together with setting the DEC algorithm so it only goes in one direction, may solve your problem.

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Usually, on most mounts that I've seen, the RA has the larger residual guiding error, not the DEC. Your RA residuals look splendid.

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And, of course, some of this advice is hard to do with remote operations.

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Best regards,

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Mark C.