Engine jerk/hiccup at idle

When at idle, about every 5 to 10 seconds the engine makes a jerk, as if spark timing suddenly changed and reset. No "check engine light".

1 year ago, distributor was replaced with new part.
part form reputable local store. Also spark plugs and wires replaced at same time.

I live looked and felt around the many little air hoses and find no leaks.

Possible dirty air idle valve?