This is just a general post to hopefully help others who have m119 engines showing low or no oil pressure at idle (but are running fine otherwise).

Car is a 92 400E that has over 160K miles.

It started showing low oil pressure at idle once it got to temperature. As in 0 oil pressure at idle and. It always peged the gage at cold start.

The successful solution was the replacement of the oil pressure sender. Put a new VDO replacement in and full pressure, drops to maybe 2.7 at hot idle.

Part is easy to change out (I did no take any pictures you don't really need any) - I changed the oil at the same time
1) remove the under engine panel.
2) drain oil
3) unplug lead to pressure sender, and break free with a 17mm open end wrench, then unscrew and remove. This is located at the base of the oil filter housing.
4) screw the new one in, tighten, and reconnect lead.
5)finish changin oil and test drive.

Some of the symptoms on my 0 oil pressure were no new noises from the engine (engine would have likely self destructed if it actually had 0 pressure). Gage would go to 0 at hot idle, and about 2.8 hot on the highway. Sometimes at that point it would still show 0 at about 1500rpm. Also the gage would do some strange swings as well.

When this first happened I tried replacing the oil relief valve, this had no effect in my case but I now know that my oil relief valve should be fine in the future.