Hi Willie

A couple of things I did when having the same problem. In addition to
the capacitor, I ran a separate ground wire from inside the airfilter
box out to the body. I attached the ground inside the box where the AFM
bolts to the air box. This seemed to make a difference. Also check the
under the cap of the AFM, a 4" sq black lid. Check to see if the carbon
track is worn thru in spots. Mine was. Took needle nose pliers and bent
the contact arm so it moved about 1 mm, moves on a fresh track now.
Idles much better.
One other possibilty is the ICU (behind the right taillight). When they
go it results in surging and all kinds of things. Before mine reached
that point, I believe it affected extended hwy driving, especially when
I took my foot off the throttle. I replace mine with one from the
wrecker. New they are quite pricey.
Sorry I can't tell you for sure what helped what because both AFM & ICU
problems happened about the same time. No problems since though, thats
been 10,000 km. Good luck.

R.Feuerriegel
88 syncro