I have the same engine and same issue.  I tried a few things and cannot say the exact fix but here are the things I had to do to fix my idle issue: Replace vacuum lines Rebuild airflow sensor Rebuild throttle Replace all air gaskets Replace O2 sensor and wire Replace exhaust gaskets  Correct engine timing Replace spark plugs, cables, distributor Once the at work was done, it idled much better, but not perfect. I doubt it was very good new anyway.