2001 camaro 3800 eng. when eng is cold oil pressure is high after warms up oil pressure drop very low at idle. why??

It is possible that the low oil pressure when idling in your 94 Dodge Dakota 3.9 could be caused by either a faulty oil pump or a faulty oil pressure sending unit. It is difficult to accurately diagnose the issue without further information and a proper inspection.

Different engines can show different values. Sometimes it is the sensor itself that causes the variation. The pressures that you are witnessing are well within operation norms and are nothing to be worried about. As long as you don't experience severe drops in oil pressure during acceleration and deceleration, then the oil pressure system is working well.

Low oil pressure at idle can be caused by an engine with worn rod or main bearings due to (usually) high mileage . This however does not mean the engine is still not serviceable as long as the oil pressure is low only at idle. The pressure should at minimum get into the normal range at anything above idle speed.Not much oil pressure is really necessary at LOW speed. At low speed, as long as there is oil getting to the bearings, even at low pressure, you are OK. In a high mileage engine the oil pressure is often low at idle simply because the oil pump is turning slowly and cannot maintain higher pressure between the larger than normal crankshaft and bearing clearances. As speed increases the pump turns faster and supplies more oil and the pressure should go higher. Low pressure as long as it is only at idle is not a problem. However at higher speeds the pressure should be in the normal range. Such a worn engine can benefit from higher viscosity (thicker) oil such as 20W-50 in above freezing weather and 10W-40 in winter. That will increase idle pressure and the thicker oil film maintains a better film between the worn parts

first suspect is the pressure sending unit itself. BUT that condition can be serious and if replacing the sender does not correct the problem you need to have an external gauge attached and actual pressure verified. since you hear no noise (yet), I'd lean towards the pump pickup screen being partially obstructed. Across the board crank bearing wear is also suspect though.
Oil pressure always reads higher when cold because the oil tends to thin out a bit when warm. It should however never drop that low, 15psi is the absolute low idle pressure I accept as nearly normal on any engine.
Fuel contamination in the oil can also cause problems but is easily identified by a simple "sniff test" of the dipstick.

Could be two things, your oil pump pick tube is clog, oil pan would have to be drop to check, or your camshaft bearing worn causing low oil pressure,I would not say piston rod bearing or main bearing, cause there's no knock noise. You will have better oil pressure when cold due to oil much thicker. so I would forget about a bad oil pump.

When the oil is cold it is thinner or watery and the pump moves more oil as it turns making the pressure go up. As the oil warms up it thickens and the pump moves less oil letting the pressure go down. Increasing the engine speed makes the pump turn faster, therefore it moves more oil and the pressure goes up. Changing oil grades will change the numbers somewhat, for example 10W40 will give you different readings than 5W30. I don't see any problem with the readings you put in your posting. I wouldn't be concerned until the warm idle pressure gets down to about 30 or a little lower. Hope this helps.

Re-new the engine oil and see if the problem persists.
Low oil pressure at idle is usually a sign of a worn motor - worn camshaft and crank bearings allowing excessive oil to pass.

how low does the oil pressure drop?? is it below 40?

DOES IT HAVE A LOT OF MILES ON IT OR MAY BE THE OIL PUMP IS IS GOING OUT? THERE IS A SPRING IN THE PUMP THAT IS A BYPASS FOR HOW HIGH PSI IT MAY HAVE BROKE THAT WILL GIVE YOU LOW PSI.

I'd check to see what is in the crankcase currently; with modern multirange oils, that sounds high.
The typical operating range is from 30-60#; 10 seems low for an idle pressure but then idiot lights are supposed to trigger at ~ 4# pressure.
If it was mine, I would change oil and put a multirange type suitable for your area in it to see what influence it has. If you are in a temperate climate as I am, it might be time to change from summer to a winter range; 10W30 is good for us and 10W40 in summer (WV).