JP,
If your AMM has bad contacts between it and the plug (either because the connectors in the plug are spread apart or because they are corroded) then it can cause all sorts of wierd problems....
Have you unplugged the AMM (car off) and then started the car to see how it runs? It shouldn't run too well, but if it's the AMM then it should lose most of the symptoms you describe. it might just be luck that it stopped running when you changed the filter......i'd check it, i had some real wierd problems, like misfiring, etc, that were caused by a bad connector in the AMM plug....
They aren't *that* expensive in America, (from a wreakers), so i'd give it a go, do the test first tho and post results.....
Az