I'm sorry man....I was at work and was having a bad day.
The L28E motor is notorious for having heat soak problems after the car has sat, after running, for about 5~15 minutes. This heat soak can make the car miss fairly bad until enough liquid gas can make into the cylinders. Also, if your warm up enrichment settings in MS are way off, it can possible cause miss fires. I would not mess with your dwell as it can REALLY mess some stuff up if you get it wrong.
I also have a 240sx TB and it has an adjustment screw(hex head stud w/ an 8mm nut that holds it in place) on the oposite side of the TPS.
And as everyone else has said.....make sure your timing gun agrees with what MS is reading.