Oil presusser normal in park but drops to zero at idle

SOURCE: Oil pressure drops to zero at idle on 2002 GMC

You could have three possable problems that I can think of. 1) Your oil viscosity is too low and you need to change it to a higher level. A 5w/30 or 10w/30 oil may thin out too much when it warms up to normal temp and shows low on your gauge. 2) The preasure relief valve is partially open due to a small piece of debris caught under the seat. Unscrew the oil filter and look at the small disk that is near the threded part on the filter base. Theres a spring behind it to keep it closed so all the oil goes into the engine and not bypass back into the oil pan. Push up on it slightly with a small tip screw driver and see that it fully seats in the hole, put a new filter on, and try it. 3) If these two things don't improve the condition, get a socket for taking the oil preasure sender off and get a oil preasure gauge to test the actual oil preasure the engine is producing. You may have a weak pump in the engine. If the preasure is within good specs, I'd change the sender unit with a new one.
Let me know what happened-
Craig

SOURCE: when starting the engine the

IF OIL PRESSURE DROP ZERO YOU HAVE WORN ENGINE MAIN BEARINGS OR FAULTY OIL PUMP.. IF OIL LIGHT COMES ON BUT OIL PRESSURE NORMAL AND DONT DROP ANY THE OIL PRESSURE SENDING UNIT BAD. ENGINE NEED OIL PRESSURE WHILE RUNNING AT ALL TIMES IF DROPS TO ZERO YOU GOT PROBLEM.

SOURCE: MY 97 yukon has Rough idle, loud knocking at high torque, and oil pressure goes from 40psi to 0psi. what do you think is the problem?

Checking oil level won't tell you anything

You need to put a mechanical gauge on
the motor,you can't go by the dash for accuracy

You could have many things that need to be
done preventative maintenance wise before
you even start to diagnose the couple of current
issues

Dash Check Lights?
Codes?
Driven for two years & never worked on?

We can't guess,you need a repair shop to
give you the solution