my 99 ss is noking
Lifters don't need a week to pump up.
LSx F-Body vehicles are known for noisy lifters.
Not necessarily a 'knock', but more like a 'tick'.
Use the search function & research 'lifter tick', or 'ticking lifters', or 'tick', ..., & you'll find lots of history.
Where are you located, & what is your native language?
Don't mean to offend, but it appears English is not your first language. :o)
20psi at idle, or at a spotlight is not a problem.
Bouncing gauge needle may not really be an issue either, but you'll have to do some tests to find out if it's the gauge, or the sending unit, ..., or some other engine issue.
Da oil pressure gage ain't gonna make da ticking sound, it'll just affekt the accuracy of the oil pressure needle.
Do a engin flush and put some new good oil in......see if dat helps da tick sounds........
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