I just bought a 99 sidekick and it has a very rough idle when in drive (it's an automatic).  If I apply the gas pedal and raise the rpms to 1000 rpms or above it smooths out.  If I put it into neutral it also smooths out.  When it is idling rough the idle fluctuates 2 or 3 hundred rpms.  I'm wondering if it isn't a vacuum
 leak.  Years ago I had another sidekick and I remember having the same problem but I don't remember how I solved it.  I'm wondering if it isn't a common problem.  Thank you for any help you can send my way..  Where is the diagnostic port located.  I live in rural Mexico so resources are limited.  There is an Auto Zone an hour away.

The Sidekick's last year of production was 1998, so you need to let us know what it is you're driving - assuming a late 90's Sidekick, the diagnostic port should be under the driver's side dash alongside the transmission tunnel.