I used to have the same problem.  Even with a new engine and everything else
replaced I would fail with high HC at idle.  Finally I went to a $39.95
"guaranteed to pass" guy set up in a van with a Sun emissions tester next to
the testing station, and he said it was a lean miss.  He cranked the idle to
1050 and the mixture all the way rich and it passed just fine.  I turned the
idle back down and drove home a happy camper.  This was four years ago, and
I do this at each test now.

Personally, I think the gas today is not up to the quality our engines and
ECUs were designed for in the '80s and doesn't ignite at the lean idle
settings as well , but that is a whole 'nother subject!

Stuart MacMillan
'84 Westy w/2.1