Running rich at idle

99 Tahoe 5.7. No check engine light. Started running rough at idle (only at idle) Looking in the mirror I can see black smoke coming from exhaust. What could this be?
Thanks

99 Tahoe 5.7. No check engine light. Started running rough at idle (only at idle) Looking in the mirror I can see black smoke coming from exhaust. What could this be?
Thanks

a bad injector is very possible remove plugs see if all or just one cyl.

A leaking fuel pressure regulator or high fuel pressure can also be the problem.

//2000CAYukon