Krays:
Please see my post at
http://www.automotiveforums.com/vbul...d.php?t=323582 under the title 91 passat stalls...help.
Sounds like we have similar issues, only yours is more or less permanent at this time, and mine is intermittent.
Have you checked all of the grounds?
You have 12V at the coil? Right?
Considered ignition switch?
I too have done my heater core (couple years ago) and yes it is a bitch. I think that at the factory, they start with the heater core, and build all the rest of the car around it. There are a ton of electrical connections in the process that could have gotten stressed/not quite re-connected. So check all of your connections near the fuse panel and sttering column just to make sure that you don't have something loose or disconnected. And don't forget to check grounds.
Please keep everyone posted on what you find, as it may help us all with similar "missing spark" problems.