Rhythmic engine surge 4.8is

[stryker14]

Hello,

My 2005 4.8is, 120K miles, engine runs smooth, but at cruise there is the slightest engine surging, rhythmically about every two seconds, barely even noticeable, but it is there.

At idle there is a very noticeable change in idle speed, about 100 rpms, it does not occur as consistently as at cruise. Maybe every five seconds or so.

Engine has new valve seals, Upper timing cover gaskets, valve cover gaskets, air pump rebuild, Ccv and hoses, alternator bracket gasket, oil cooler line o rings, and all the associated items that would go with these repairs. I was hoping my issue was cause by vacuum leaks from one of the gaskets, they did not fix my problem.

I also changed the minimum valve lift, (I tried this after searching this forum as a possible fix) The valve lift was set at 1mm, I tried 3mm, and also 8mm. It did not fixed or change my problem.

No engine fault codes from INPA.

Anyone have any ideas?

Could it be a Mass airflow problem? Any other common vacuum leaks? Vacuum Lines look good. Help please!?