stock 1973 318 V8 starts but won't idle without foot on pedal

Engines fired up after sitting for 25 yrs [ & a lot less than 25 yrs...] can develop a multitude of different problems. I was called to have a look/listen to an engine, similar circumstances, & a couple of valves had rusted in the guides, causing piston contact & bent valves. Engine still ran, but roughly.