I wouldn't mess with the distributor unless your planning on timing it correctly. Get a timing light and you should also take a look at your air/fuel ratio when you do the timing. This also could be an issue with the idle setting on your throttle body. In the Bentley (if you dont have one get one) there is a section that discusses checking the idle setting using a dwell meter.
I think a good starting point would be to remove the ISV and clean it up a little and see how it runs.
Do you have a timing light?
Are you familiar with where all the timing marks need to be on a 16V?
Do you have a harness that you can put onto the DPR (differential pressure regulator) on the firewall side of the fuel distributor?
Do you have a multimeter?