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I think I will use this modification.
That the light is on tells you there's an issue.
Weak pump, or wrong viscosity oil. You may also want to check that the engine number matches the Car Pass/VIN data to confirm that the engine hasn't been replaced with a potentially much higher mileage one than the odometer might suggest.
There are plenty of other causes of the issue:
low oil level, wrong oil grade, worn component(these three are the most likely given the described symptoms), faulty switch(remember it's on/off), damaged wiring at the switch and others.
If the oil grade and level are correct(there's no reason to use anything other than 10w40 on a used engine), and the light goes out as soon as the revs rise off idle, then I would suggest there's nothing to worry about - this is how millions of engine have been used for decades
Today I removed little sump. I didn't find any metal crumbs inside. So now I decided to use engine like it is.If the oil pressure drops even more, only then we will try to restore the oil pump (I have another not working engine which ended because there was no oil presure 
) . Because removing for now it is too much work.
Something to consider, not all EPCs show the subsequent parts, and not all parts sellers have the presence of mind or ability/inclination to look beyond the "Discontinued" label. Leaving you to guess what the replacement might actually be.Might also be worth checking the oil pressure relief valve while you're at it, although I can't remember where they are on this engine.Maybe, plus I changed to not to same switch. Stock switch is this :
Blocked oil pickup is definitely a possibility and worth eliminating.
Could just be a lazy oil pressure switch?
If the oil pressure picks up quickly at higher revs it's possibly not work worrying about if the above check out OK.
It's normal for some variants of the V6 to idle as low as 450-500 RPM from memory.
https://www.gmpartsgiant.com/parts/gm-sensor-90566938.html
Buts impossible to buy this part so I changed to this:
https://www.gmpartsgiant.com/parts/gm-sensor-90337695.html
Later I will try to make video with acceleration at idle.
Refit the original sensor and report back. No change means your old sensor is working normally.
Might also be worth checking the oil pressure relief valve while you're at it, although I can't remember where they are on this engine.Maybe, plus I changed to not to same switch. Stock switch is this :
Blocked oil pickup is definitely a possibility and worth eliminating.
Could just be a lazy oil pressure switch?
If the oil pressure picks up quickly at higher revs it's possibly not work worrying about if the above check out OK.
It's normal for some variants of the V6 to idle as low as 450-500 RPM from memory.
If you're using 5W30 switch to 10w40 and see if the hot idle pressure increasesI tried this weekend, increased a little bit, but its still little bit missing when engine is hot. Now its enough just to turn on AC to reach minimim stock oil pressure norm on iddle. (when rpm is 550-600 its ok) but when 500 sometimes I get that damn lamp
It might be covered in the owners manual.
Basically it can be considered normal, especially on an older engine with some hours/miles on it.
However oil gets thinner as it gets hotter, so if your oil pressure is low when the engine is fully warmed up, then there's a chance you're using the wrong oil.
Equally, if the oil pressure doesn't increase with rpm then you need to prioritise removing the sump and checking the pick up. If it's blocked, you've found the problem, but if it isn't then the pump itself could be failing.
The idle speed is non adjustable on the 3.2/2.6/2.2 but 550rpm rings a bell as being normal.
how many miles/kilometres are on the car? Low oil pressure at idle can be due to worn main & big end bearings ...but I have this problem only on hot engine, and after driving some time.
It shouldn't be idling at 500rpm, though.
how many miles/kilometres are on the car? Low oil pressure at idle can be due to worn main & big end bearings ...
I added video. (in that video I accelerate a litle bit, after some time I realesed accelerator).
