350 SDL Idle - Sometimes Rough/Sometimes Smooth?
 

1991 145K miles.

Always idles rough first minute or two when cold. Once warmed up idle can be smooth other times it is rough with injector knock (sounds like one cylinder with the knock to me).

Pre and main fuel filter replaced with no change. Car runs great otherwise. I am the original owner so I know the history of the motor (no significant problems to date).

Any ideas on a possible fix appreciated.

Thank you.

Check your timing chain