The oil pressure is low at idle and rises with higher engine revs. Oil levels are ok, new oil approx 2000kms ago. Was a slight noise at one stage in the engine but went away after engine's revs in

put oil in the engine

It is not a big worry if the oil light comes on at low idle, but it should go off as soon as the revs rise a bit. I'd recommend

- change the oil AND FILTER with the correct grade, to the correct level.
- ask a mechanic to temprarily replace the oil pressure sender with an oil pressure gauge, and with the engine HOT, rev the engine up and down to see what pressure there is. You should have roughly 10 psi per 1000 RPM.

If the pressure is very low, ask the mechanic to check the oil pump and engine bearings. If you are not burning oil with lots of blue smoke from the exhaust, it is unlikely the bearings are worn.
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There should not be any pressure.

Have you checked oil level?

This is not necessarily a problem. If the oil is at correct level and viscosity grade, and the light always goes out with a small (not large) rise in revs, then it could possibly be OK. An engine does not need much oil pressure at idle, say 600-800 RPM.

It could also be a faulty sender unit on the engine, a worn oil pump, or a faulty oil pressure relief valve on the oil pump or in the filter.

To be sure, get an oil pressure gauge fitted to the sender outlet hole, and see what the reading is at various revs. If there is indeed a pressure problem by the gauge, try first a new oil filter. If not it is probably a faulty sender unit.

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

i would say the car is safe to drive.IF the pressure sensor was working correctly, and your engine was a complete dog, then you would expect there to be some loss of oil pressure, but not 0 to 4bar in a blip of the throttle.given that the oil pressure sensor is a common fault (and it controlls the oil pressure light, it is not a seperate switch), i would say the sensor has a 'dead' spot on it, and a blip of the throttle just sees it outside the dead zone of its reading, and pings back to 4bar (its natural to get a slight rise in oil pressure when higher revs are acheived). 4bar is the right value, its what mine sits at. maybe a tiny bit under (3.95) when the engine is very hot/in traffic the oil pressure is reading just over 4 at all times, dosent go up or when accelerate or down at idle is this normal, used to mercedes W124 where it can register .3 up on idle but when accelerate it should goto max, ie 3 bar Whats the mileage on the car. Sounds like It certainly is suffering from low oil pressure at tickover, but loads of cars do and continue running for thousands of miles. blue/white smoke on start up and that points to valve seals and, yes, the head would have to come off to replace them, but it's normally just blue smoke. White smoke points more to head gasket, but that would be replaced anyway when doing the valves.Bet the engine sounds smooth as silk too
Oil pressure is determined by the rate at which oil flows through the internal combustion engine of a car. Low oil pressure is a real danger for engines, as it indicates that the bearings in an engine have worn, allowing the oil to flow more easily and at a lower pressure. However, high oil pressure is generally not a concern for motorists. Oil pressure fluctuates with the heat of a machine, and though high oil pressure can indicate a serious problem, it generally means the engine is in an adjustment period.Oil Pressure at Idle For many cars, oil pressure is much higher upon start-up or while idling. The reason for this has to do with the temperature of the engine. When an engine has been sitting turned off, it cools down, as does the oil that flows through the machine. Upon start-up, the engine temperature begins to rise. As it rises, so to must the oil heat up to find a level pressure to flow through the machine. Cooled oil is thicker, causing it to flow more slowly and at a higher pressure through the machine, until it reaches its optimal operating temperature.Pressure Relief Valve Recurrent high oil pressure, even after the machine has been running for a while, can indicate a problem with the pressure relief valve. The pressure relief valve is responsible for regulating oil pressure throughout the internal combustion engine. It is a safety device intended to keep vessels or piping from experiencing extreme pressure. When this device is malfunctioning, it will cause high oil pressure in an automobile.Types of Oil The type of oil put into an engine can also account for extremes in oil pressure. Low-weight or thin oils will operate with low oil pressure, as they will pass through the machine quite easily. Thicker oil will pass through the machine at higher oil pressure readings. Generally, after an oil change, when fresh oil is introduced into the machine, oil pressure will increase. This, however, is only a sign that the oil that formerly operated your car was too thin for optimal performance.

try slightly over filling oil level if engine starts and runs for a minute or two then dies the oil pick up in sump has fallen out (cracked mounting bracket) or sucking air instead of oil. you can remove small tin engine sump after draining to check oil pick ups, after confirming it runs ok for a little while once over filling oil level in engine.
another thing that goes is the rail oil pressure sensor which reads incorrectly and a tell tale sign this is broken is the injector loom connector is full of engine oil when disconnected this is near engine oil level dip stick(wiring loom comming out of rocker cover), the sensors reading can be checked with scan tool before starting with ignition on, (0-0.2MPA) it must read if its reading higher with ignition on only (motor not running) the sensor needs replacing, the engine ECU needs to see approx 200MPA when cranking to get injectors to start to work properly and higher when running at idle and beond (up to about 5MPA at higher revs) if this is not getting to this or readings are fluctuating badly indicating air in oil the injectors wont supply the correct amount of diesel. in which the engine oil comming from low pressure (pickup pump) to then high pressure oil pump to rail and injectors.

Did you try changing the actual oil pressure gauge?

Had exactly the same problem, completely baffled us until we discovered that the it was the oil pressure switch. We had already replaced it with a new one and then that didnt fix it so we fitted a new oil pump, but as soon as it was revved over 3000 revs the oil light came on. It turns out that there is actually a choice of 2 oil pressure switches for this car (1999 1.4 polo) one works only low pressure (black cap) and is the wrong one, the other works on a higher racio (green cap) its the high pressure one you need. If the oil light was on at tick over or below 3000 revs then its the lower oil pressure switch needed, above 3000 its the higher one. The parts people insisted there was only one, but there is definately a choice of 2 and it fixed ours instantly.
If it was an older model they actually have 2 switches on the car itself and one is a high pressure and one is a low pressure (just incase anyone needed to know)