95 Jetta-PLEASE HELP-Loud Pop When Started in Cold Weather

:frown: I just had another engine put in (2.0L manual transmission). The Jetta is a celeb editon four door. It had a full tank and was running fine and I left it at my parents house during a snow shower. 2 days after (still cold weather), I came to get it and when I started it, a loud pop happend and now the car will only start/turn over but not stay running. The engine was in for about a month. Got it from a well respected VW yard. The guy who put it in was a good he builds cars for a living. He is very hurt and cannot look at my car. I look on other postings but nothing like my issue. Could it be Distr. Cap or Fuel injector/filter? I got to get it running for work. Thank you.

I added more info and still don't know what it could be and now someone busted the passenger side window out. :banghead: