Oil Slug is one of the main causes of a lifter tapping. Something that would up help clean the slug would be an Engine Flush, called Auto-RX. I have never used it but have heard many good things about it and it is made in the USA. Hope This Helps.
A loose rocker arm for a valve mite be a easy fix with a valve adjustment
A bad EGR valve should not cause the engine to not start. There is most likely another problem that is causing the engine to not start.
EGR VALVE IS LOCATED NEXT TO THE TOP RADIATOR HOSE AT THE ENGINE, IT CAN CAUSE ENGINE TO MISS, STALL AND SURGE.
The PCV valve on a 2002 Chevy Suburban 6.0 liter engine is located in the engine. You cannot miss the valve.
Cold engine it's the oil filter, get a high end filter with a pre lube valve. Hot engine cheap or wrong weight oil, or, bad oil pump.
Could be--valve not closing completely
The EGR valve on a 1994 Chevy 1500 is located on the top of the engine. If the valve becomes stopped, the engine could idle rough or stall.
Engine running hotter then 220 degrees can cause valvetrain noise. Bad fuel can also cause valve noise / PINGING sound. Ignition timing to high / Advanced to far, can also cause engine noise.
Tapping in a diesel engine often means a valve lifter is beginning to fail. It can also mean that sub quality fuel is being used.
metallic tapping that becomes faster as the engine speed increases indicates valve tapping. one or more of your valves clearances are misadjusted. to help you find out which one it is cut a small section of hose, put one end to your ear and place the other end on different spots along the rocker arm cover, where the sound is loudest is where the problem valve is. purchase a repair manual for your car for valve clearances and specific valve adjustment procedures.
Worn valve train starting with the camshaft lobes.
The 1999 Chevy Geo Metro 1.0 liter engine PCV valve can be found on top of the engine. The PCV valve will be behind the air cleaner housing.