When I pull the spark plug knocking sound goes away and engine runs more smoothly and less vibration at idle. However I thought rod knock gets louder with higher revs?
With higher revs the engine runs a bit smoother. Compression on cylinder 3 is within 5% of the other cylinders.
I did valve adjustment and when I put everything back, engine idle is rough. Sputters a bit but keeps going but lots of engine vibration.
Any thoughts if it’s rod knock or something else?
My "uneducated" guess is something else. Setting aside the bothersome noise, what prompts you to assume that your engine noise is a rod knock? Is the engine seriously worn with low oil pressure? A rod knock may be alarming, but it is not necessarily accompanied by a misfire or “rough running.”
Your description of the problem is difficult to follow and suggests a problem unrelated to a rod knock. You state that when you pull “the” spark plug, (1) knocking goes away and (2) engine runs more smoothly and less vibration at idle. Are you describing each cylinder or are you focusing on one specific cylinder? Are you removing the high tension lead to the spark plug to disable that cylinder, or are you removing a spark plug? If you are somehow disabling a single cylinder by disconnecting a spark plug lead, it is hard to fathom how that would result in an engine that “runs more smoothly and less vibration at idle.” Ordinarily, if disconnecting a spark plug wire results in a smoother running engine, that “possibly” suggests a mixed-up firing order and crossed spark plug wires.
You state performing a valve adjustment, “and when I put everything back, engine idle is rough.”
Was the engine idle rough before the valve adjustment? To what values did you adjust the valves?
Was the adjustment performed cold - or hot?
In another post you state: “I did use a stethoscope and sound seems to be coming from top end?” Later you say: “I put all the belts back and knocking sound comes back. Used stethoscope and it’s not power steering pump, nor alternator, nor water pump.” A rod knock is apt to be loudest where each individual rod connects either to a piston or the crankshaft. Have you directed your scope near these areas? The fact that you apparently hear a noise “only” when accessories are connected would suggest that is where your (perceived) problem lies. Since alternators, power steering pumps and even water pumps can make noise due to worn bearings or sloppy mounting bushes,
perhaps one or more of your drive belts is/are too tight.
From your description/s I still do not know whether you have directed your stethoscope to the mid/lower portion of your engine - for abnormal resonance. (Often overlooked is a worn/slacked oil pump chain and/or related parts. Yes, chain slap tends to be louder or more easily heard - at idle.)
