My oil pressure drops big time at idle
 

My oil pressure drops to almost zero at idle...according to dash gauge. Throws the check gauges light. 138k miles, great compression, no oil burn, very very very slight valve tap at idle. Oil is 10w40

Oil pressure switch is probably bad. I just replaced mine as it was leaking by into the wiring harness making it seem I had low or no oil pressure at idle.

Uh-oh
 

Bad rings = smoke at tail pipe
Bad bearings = low oil pressure

Try the cheap fixes first, sending unit, gauge, etc

Are you the original owner?

Good luck