Diagnosis steps & tools?

[Terrill Yuhas]

I have a '90 Chevy Beretta with the 3.1L V6 that I'm looking for some
diagnostic suggestions.  Basically when the engine is warmed up, it hunts
for an idle.  It never stalls but it sounds like it's misfiring.  I'm in
the process of figuring out which scantool to get so I took it to the
shop.  Mr. Goodwrench ran some diagnostics and said everything was fine.
I took the service advisor out for a spin and showed him what it was
doing.  His reply was that this is something that is designed in.

The biggest problem is I'm now getting close to failing idle emissions
tests so I figure this isn't really a "designed in" idle hunt.  Rather
than chase it with parts, I'm looking for any suggestions on where/what
tools to get so that maybe I can see what's going on.

I don't know which scantool is adequate.  I was looking at either the Auto
Xray or the Actron Scantool.  The others I saw were thousands of dollars.
Not knowing what a "Mr Goodwrench Diagnostic" consists of, I wonder if any
of those hobby scantools would tell me anything.

I also looked at the Diacom but I always get ten-year-old brochures when I
contact them for info.

I've been toying around with EFI for a little while, so I figure this will
really get my feet wet!

Thanks,

Terrill