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535is Driveability

          Time for net wisdom again.

          My '87 (July '86) 535is is 'stumbling' around 2000 RPMs
          while cruising.  It is worst at 2002 RPMs (Fruedian slip
          ^8), but acts up in a band few hundred higher or lower RPMs.
          It basically feels as if gas was stopped for a fraction of a
          second or there was no spark.  Under acceleration it is not
          noticeable at all and performance seems as good as it ever
          was.  It happens with cruise control on or off, flat
          surfaces or hilly as long as a steady speed is being
          maintained.  It first started almost two years ago but
          pretty much went away (i.e. less noticeable) when the O2
          sensor was disconnected.  It has progressively gotten worse.
          In the last six months it has started to have an oscillating
          idle for the first 30 seconds when I start the car, but I
          think that is the ICV and the fact that I only drive it once
          every couple weeks.  Here's what I've done so far.

          Swapped DME's with no effect - my car and swapped car
               behaved as they did before the swap (He had my chip
               though ^8).
          New fuel pressure regulator
          New in tank fuel pump
          1 year old external fuel pump - problem started before this
               was replaced anyway.
          New fuel filter
          New O2 sensor
          New MSD coil from the 2002 didn't help
          New Bosch silver plugs
          New air cleaner
          Valve Adjustment (Checked oiler bar bolts again ^8)
          New distributor cap and rotor
          Spark plug wires appear OK, have same resistance (around
                5.5k ohms I think) - they are four years old, about
                25,000 miles
          Air box seems to move freely by hand - I am going to try
                swapping this also to see if it makes a difference.
          ICV was cleaned, didn't help oscillating idle
          Checked for vacuum leaks using the carburator cleaner
               method.  NO noticeable increase in idle on any hose or
               fuel injector seals.
          Have run two bottles of Techron through - no noticeable
                effect

          I'm down to air box, bad injectors, a vacuum leak I can't
          find or CO mixture which I will have to take somewhere to
          get adjusted.

          As you can see, I'm no mechanic.  I'm a parts changer.  Does
          anyone have a clue what the cause may be?

          matt

          '75 2002 Erector set
          '87 535is w/ Dick Van Dyke syndrome
          '88 M3
          '87 Mustang LX 2.3l w/ auto.  Hey, at least when I turn the
               key it works.