Low oil pressure while car is in idle..check gauge light comes on. I had the oil pump replaced and the sludge cleaned up. The check guage light still comes on when car is in idle and epecially when the car is hot.

Could be a faulty sender unit, located near the oil filter , remove it and connect a pressure gauge, check the pressure at idle and at speed both cold and hot if Ok replace the sender unit , if still faulty check the oil pump and relief valve.

The oil pressure light coming on at idle is not a big worry, so long as it goes out as soon as revs rise.. First step is to remove the oil pressure sender unit and screw in an oil pressure gauge. a mechanic can do this for you. This will tell you if the sender is faulty (common enough) or the oil pressure is low. A rule of thumb is to have about 10 psi per 1000 RPM in the normal rev range

If it is indeed low, possible causes are
- worn big end or main bearings (the car is old enough)
-faulty or weak over-pressure relief valve in oil pump
-worn or faulty oil pump
-blocked or sludged up oil passages
-blocked or sludged up oil pickup strainer mesh in sump

Some of these can be investigated by putting the car on a hoist and removing the sump
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The oil pump in the pan is worn and needs to be replaced. Idle speed will not turn it fast enough to pump up the pressure. Common problem.

If your oil is clean and not sludged up where it restricts oil passages, then your low oil pressure may be caused by worn crankshaft bearings. Does it burn any oil? Lotta miles?
You need to know the true oil pressure reading. Have it checked with a gauge and go from there. Your oil pump may need replacing, or sometimes a good top oil treatment may clear out the passages and restore oil pressure. Good luck.

Oil pressure always changes with rpm.
At idle you should have around 10 psi, and it should max out at high rpm around 50 psi or so.
You not only can't have as much pressure at idle, but you don't need it either.

Very first thing you need to do is install a mechanical pressure gauge on there to verify what you see on your gauge. If the actual pressure is low, then it's time to start looking inside the engine. If not, then you need to trace out the electrical problem but will know the engine is safe.

If by pulsing you mean that the idle is fluctuating up and down, this is caused by oil/sludge build up in the throttle valve. To rectify this remove the intake pipe at the throttle valve. Use engine cleaner/degreaser on a rag to clean out throttle valve around throttle butterfly. Open butterfly manually to assist access. The oil pressure light coming on is usually caused by the oil pump pick up becoming blocked by carbon and sludge in the oil sump. If you have a suitable oil pressure gauge, check the oil pressure at the oil switch. Oil pressure should be 3.5- 4 bar at 2000 rpm at operating temperature. If pressure ok, Pressure switch may be faulty. If pressure low you will have to remove oil sump and clean out or replace oil pump pick up. If not done, may result in major engine damage. Sludge and carbon build up caused by oil not being changed often enough. Best to use a synthetic oil.

need to find out the pressure the pump is putting out hook up a mechanical pressure gauge most use the sensor port to hook into and test pressure if pressure good than u may have a sludge problem where a flush might help-if pressure low possible clogging [sludge build up] of oil screen-[which a flush or back blow-compressed air -to clear or clean pick up tube and screen should help ]--or internal engine problem or oil pump bad

The sending unit for the oil guage will cause the oil guage to fluctuate this is caused from some sludge build up that is more than likely stuck in the sending unit tube. Use Gunk motor flush on your next oil change this should help the oil guage problem.( make sure you read the direction on the back of the bottle)
As for the check engine light you can take it to Auto Zone and have them scan the computer. Sometimes the EGR valve will build up with carbon causing the valve to stick slightly open which will make the idle on the car fluctuate up and down. Its also possible you need O2 sensors.

I have a 1999 dodge ram with a 5.9liter. Come to a stop and bam no pressure. Replaced sending unit twice. First after market, then mopar. Problem is still there. Replaced pump. Problem was still there. So I talked to tons of dodge mechanics, and this is the real problem. Who ever said that these engines are none for sludge is just reall really stupid. BOTTOM LINE ON THAT FACT. Sludge comes from neglect...
Dodges oil pump makes 8-10 Psi at idle. Always mechanically test that no MATTER what. But the sending unit needs 12-14 psi to read it. So what happens is the engine warms up, and the oil thins. Then you come to a stop, and rpms are low, and your not producing enough psi for the sending unit to read it. So your truck is fine. But if the chime is getting to you. Install a high volume pump. I returned the stock one, and got the high volume pump. I will bet if you change your oil every 3,000 miles you will not see sludge at all. If your dodge has high miles replace valve cover gaskets, becauce the high volume pump may cause the gaskets to leak. Whoever said ther none for sludge just has no love for a dodge, or is a moron mechanic that is stuck in his ways. High volume pump is the fix $85.00 plus pan gasket. If you have a 4x4 you can do it yourself. Drop the starter. Remove torque converter cover. With a 13mm socket with a variety of extentions, and removing a dozen bolts. Do it yourselfer will complete it in 4 hours....