1998 Ford 4.2L V6 idle issue

Just got a 1998 Ford F150 with the V6 / Auto about 100K miles. Not sure when its had a tune up, but occasionally at a light the idle will reduce as if its about to stall, then it recovers.
Recently I let the vehicle sit a few days without a start and it started up fairly quick, but soon the idle slowed down quite a bit again, nearly stalled.
Some internet research says it could be an EGR valve and other things like the coil pack module?
I was gonna try some STP fuel injector cleaner maybe as a start....any good resources out there of this engine?