It sounds like you may have a broken valve spring. Hi, my name isXXXXX to Just Answer!.

A broken valve spring will allow the affected valve to "float", never coming back to its seat. Loss of compression in that cylinder is a given, but the second effect of a broken spring is that exhaust gases are pulled through the same cylinder, emerging in the intake manifold... where these oxygen-poor gases pollute the intake supply for neighboring cylinders. This would explain the extremely poor ldle you're seeing as well as the heated intake ports.

Try to determine which side of the engine the problem originated and pull the valve cover for inspection. Knowing that the intake ports heat up is a big plus in diagnosis.

There is always a possibility of having a bent valve from a broken spring event like this, but it doesn't always happen. If you find that engine compression when tested at cranking speeds is normal, chances are very good that no permanent damage has occurred and the opposite is true if you find a cylinder with no "squeeze"... it's probably smacked the valve. Low speed rotation (like during a compression test) will often give the valve time to return to its sealing position even in its weakened-spring state.

If no valve damage has occurred, the (presumed) broken spring can be replaced without cylinder head removal. Special tools designed for Hemi valve and pushrod service are a big help, but it can be done with more conventional tools as well.

Check it out and let me know if you have any questions or problems. I'll be glad to help.

Good luck!

Ed