'88 2.1l Vanagon Wolfsburg

Recently started having troubles with hesitation during acceleration in
the afternoon when heading home from work.  Makes you think twice about
when to pull out into traffic.
Routine works out like this...
No problems with idle stability and no hesitation in the morning on the
way to work.
After the van has sat for the day and I start out for the trip home the
idle is acting pretty erratic(500-900) and the van hesitates when
accelerating from a stop.  Almost feels like its starved for fuel.
This hesitation goes away after a few miles or so but the idle remains
erratic and I experience a slight bucking but pretty rarely.  Not the
vanagon syndrome type of bucking
All of these symptoms happen in the afternoon and are gone in the
morning.

Replaced the following due to other issues and preventive maintenance
less than a year ago
O2 sensor
Temp II sensor
spark plugs
rotor
dist cap
plug wires
fuel filter

Idle Stabilizer Valve is humming but of course I can't tell what its
doing while I'm driving
Ran 4 oz of Marvel Mystery Oil in the gas for 2 tank fulls
Plan to check continuity of plug wires and condition of plugs on
Saturday.
Replaced and soldered new ground connector for Hall Sender.
Inspected Hall sender and no signs of connector cracking or broken wires

Would appreciate any advice on where else to look.  Searching the
archives resulted in too many dead ends or discussions about vanagon
syndrome

Thanks
Barrett Willet