Saab: 1989 saab 900 wont move or start, mass airflow sensor, coolant leak

Question
Hello,

I just changed out the alternator because it was killing the battery quickly. I started the car and it ran but with a thick smoke coming out the tail pipe that smelled of gas so I assume there's an air flow problem? The car then died after running for about 20 minutes and would not start again. Also with the car off and in neutral the car seemed lock and I could not push it even on the down-hill slope it was on. It feels like the transmission is locked?? Any ideas on this issue?

Answer
Dan:
To help with the diagnosis I need to ask:
  What color is the smoke?  If bluish, its an oil burning problem; If whitish, its likely a coolant leak (possible headgasket); if blackish, its likely an over-rich fuel problem, which could be caused by a bad spark plug, stuck/defective fuel injector, faulty mass airflow sensor,or stuck-on cold start control for starters. (other less likely causes are possible) Also, when the engine DID run, was it smooth or irregular?
Feel free to get back to me with your observations so that we may proceed with the diagnosis.
  Hope this helps,
         Jerry