2001 hyundai tiburon. Runs like fouled plug or bad valve

Injector clogged , plug fouled, weak coil , bad plug wire if not coil on plug , weak compression on that cylinder from bad rings, valve seat or head gasket .

Does it give blue smoke from tailpipe when first started? If so, bad valve guide seals are letting oil slowly seep into cylinders overnight, fouling plugs on startup.

there are only four possibilities left:
1: valves are not fully seating - adjust rocker arm / cam
2: piston rings are bad - replace rings
3: holes in pistons - replace
4: cylinders out of round - most complicated repair, bore / machine cylinders and replace piston rings with oversized rings.

of course you could just have 'gunk' on the valves preventing full closure........

Sounds like a bad throttle body.

1342

My 2001 Daewoo Laganza also showed this problem. It turned out that my valve cover gasket was
not seated properly and oil was accumulating around the spark plug of the #3 cylinder. Replaced gasket and engine started running fine.

Yes, I think that the valve is either broken, or the rings are worn out on the cylinder. More likely a bent or broken valve or stuck valve in the open or closed position.

I would use a compression tester, though, to test how much pressure builds up in each cylinder and to see if it is balanced across the remaining cyilinders.

Many new cars hide most of the engine underneath plastic covers that must be removed to find anything. The smoking problem may or may not be serious, but it's likely that the spark plugs will show black oily deposits on the interior insulators. Cleaning or replacing the plugs will usually make the engine run ok for awhile, but with continued smoking, it will foul the plugs again. If all the plugs are fouled, then look for something like a bad PCV valve that creates crankcase pressure when plugged. Worn out valve seals which allow oil to leak into the cylinders can account for smoking only on start-up. These seals can usually be replaced without pulling the cylinder head. Hope this helps!

u damaged the valve train or damaged a piston--blue smoke means ur burning oil pull the plugs to determine which cylinder[s] is or are affected the plug would be fouled or have build up on it and do a compression test --possible problems--bent valve--burnt valve-bad valve guide --bad rocker- bad lifter- valve spring broken

it looks like 3 of your cylinders are only working with the 4th one working every once and a while, what kind of plugs do you use? I find the Platinum 2 Bosch spark plugs are the best to use. Hope you figure it out, brst of luck!
Sven