2001 tundra low oil pressure at idel engine warms up what does line on gauge repersent in lb how to fix or is it normal 90,000 miles obit always did since m

Do not drive the truck until the issue is resolved.

1. Make sure the oil is at the proper level in the engine with the correct spec oil for the pickup. Oh it is normal for the oil pressure to be a little low at idle and go up to the normal range as the engine rpm goes up to normal operating range.

2. It could be either a real problem or a problem with the oil pressure indicator. To verify which connect a mechanical test pressure gauge of the proper range say a 0-100 psig scale to the point where the oil pressure sensor is connected. After it is connected test run the engine for a short period. If the pressure shows normal replace the oil pressure sensor. If the gauge confirms the low oil pressure then you have a serious issue in the engine. It could be:

1. Bad oil pump or oil pressure relief valve

2. excessive clearance in the bearings due to high miles.

Low pressure when at idle, after the engine has warmed up and the oil has thinned, indicates that the oil pump is worn and needs to be replaced.

Remove the oil pressure sending unit and have a test gauge hooked up and see if the sending unit is defective. If you really have low pressure the engine should be making lots of noises.

see this tips and fix it. God bless you
The oil pump supplies oil to lubricate your engine. If the oil pump is worn or is not turning, the engine will suffer a loss of oil pressure, which may result in engine damage or engine failure.
The first sign of trouble may be a low oil pressure warning light, a drop in the normal reading on you oil pressure gauge (if your car has one), or the appearance of ticking or clattering sounds from your engine.
As a rule, most engines only need about 10 PSI of oil pressure for every 1,000 RPM of engine speed. Oil pressure will read higher than normal when a cold engine is first started because the oil is thick. Oil pressure will gradually drop as the engine warms up and the oil thins out. So normal oil pressure on a warm engine cruising down the highway is typically 30 PSI up to 45 PSI.
SYMPTOMS OF OIL PUMP TROUBLE
The first thing you should do if any of these symptoms occur is to stop your car, turn off the engine, let it sit for a few minutes, then check the oil level on the dipstick. If the oil level is at or below the ADD line, add a quart of oil to bring the level back up to the full mark. Add as much oil as is needed to raise the level to the full mark. Then restart the engine. If the warning light remains on, or the oil pressure reading does not climb back up to its normal range, or the engine noise does not go away, you may have a bad oil pump.
The other possibilities include a bad oil pressure sending unit, or a problem with the oil pressure warning light circuit or oil pressure gauge.
OIL PRESSURE SENDING UNIT
If the engine is NOT making any unusual noises and seems to be running normally, and the oil level on the dipstick is FULL, but you are still getting a low oil pressure warning light or low gauge reading, the fault could be a bad oil pressure sending unit.
The oil pressure sending unit is mounted on the engine block. On some applications, there is a spring-loaded pressure-sensitive diaphragm with a switch inside the sending unit. This switch completes the circuit to the low oil pressure warning light if oil pressure drops below a certain threshold. The unit may stop working if the diaphragm inside fails, if the switch is stuck, if the small hole that allows oil to enter the sending unit becomes plugged, if there is a loose, corroded or broken wiring connector at the sending unit, or there is a fault in the wiring circuit between the sending unit and warming light.
On vehicles that have an oil pressure gauge (electronic, not mechanical), the oil pressure sending unit has a small rheostat inside that sends a variable voltage signal to the oil pressure gauge when the diaphragm moves. A worn spot on the rheostat or any of the other problems just described for the simple pressure-type oil pressure switches can cause a problem.
FORD'S FAKE OIL PRESSURE GAUGE
On many Ford vehicles that were built from 1980 through the 1990s, the oil pressure sending unit has two switches, a low pressure and a high pressure. These vehicles also have an oil pressure gauge, but the reading on the gauge is not a true indication of real oil pressure. As long as the pressure to the sending unit is between high and low, the gauge will read normal. If oil pressure drops and trips the low pressure switch, the dash gauge will now read low. Or, if oil pressure goes up and trips the high switch inside the sending unit, the dash gauge will read high. Consequently, don't rely on the oil pressure gauge for an accurate reading in these vehicles. It is only a gross indication if the oil pressure is low, normal or high.
OIL GAUGE PROBLEMS
If the engine is NOT making any unusual noises and seems to be running normally, the oil level on the dipstick is FULL, and you have replaced the oil pressure sending unit but are still getting a low oil pressure reading on the dash gauge, the fault could be in the wiring circuit between the sending unit and gauge, or the gauge itself might be bad.
Check the wiring connections on both ends as well as wiring continuity between the sending unit and gauge. If no wiring faults are found, hook up a pressure gauge directly to the oil pressure port on the engine and check oil pressure with the engine running. If the engine-mounted gauge shows normal oil pressure but the dash gauge is reading low, the problem is a bad dash gauge.
On the other hand, if the engine-mounted pressure gauge reads low and you have done all of the above, chances are the oil pump is worn, or it is not picking up enough oil because of a restriction or blockage in the pickup screen in the bottom of the crankcase.
OIL PUMP PICKUP PROBLEMS
The pickup tube has a screen on the end to prevent large chunks of anything bad that ends up in the crankcase from being sucked into the pump. But we are talking BIG chunks of debris, not normal wear particles or carbon or dust or other microscopic-sized abrasive particles that can cause pump wear over time.

A "tune up" is not rquired on this engine, the computer makes al necessary adjustments, there is nothing to adjust. Possibly spark plug replacement if it's a V-6 they should be replaced at 30,000 miles the V-8 engines use iridium plugs which last about 100,000 miles, the timing belt on both engines should be replaced at 90,000 miles, replace the air filter every 30,000 and change oil and filter at 4,000 miles. I would aslo recommend cleaning the carbon out of the throttle body at around 60,000 miles to prevent low idle and stalling.

You can't trust the light sensor, so you need to get a mechanical gauge. A cheap capillary tube one is only $10.
You should also change oil.
If the engine has over 100,000 miles, you could consider 20W-50 oil.
You could also have a problem with fuel or ignition, causing oil dillution.
Does it look too thin or smell like gas?
It could also be the oil pump is bad, but that is not normally worth trying.
The number of miles on the engine would help.
But low idle oil pressure is not that important.

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.

If the valve lifters are quiet you most likely have oil pressure even with gauge showing "0".Sounds like the oil pressure switch going bad.I would try that first.

Nope, normal on start up is 60 PSI and once warmed up drops to 45 psi. Have the oil pressure checked for a proper reading during start up's when the engine is cold. As for the lifters ticking, that may be a sign that the engine was ran with low oil pressure or no oil and the lifters are damaged, or low oil pressure and the lifters are starved of oil. Try not to drive it and have a proper oil pressure reading, low oil pressure will damage the engine by having the main crank bearing to spin which is a engine replacement. Good luck and keep me posted.

Two things...when it reads zero, is there any engine noise (tapping or knocking)? After you rev the engine does the pressure read normal at idle and function normally, or does it go back down? Either way, you should not drive the vehicle 'till you have a mechanical gauge (yours is electro-mechanical) put on there and the actual pressure is tested. The condition may be a bad sending unit, a bad bearing or possible obstructed oil pump screen. The repair is obviously different for each one and the price is as well.