So does it start or not? If it runs for a few seconds then it starts. Maybe its not
getting fuel. Listen for the fuel pump running when you switch the ignition to the
on position. If the pump runs check the fuel pressure to see if there's adequate
fuel making it to the engine. While you're at it scan the car for trouble codes.
Have you load tested the battery? If boosting it makes it turn over maybe the
battery is worn out. Did your cleaning of connections include the various grounds
that are on the car? Any or all of these things could be causing you problems. It
could also be something totally unrelated to any of this, which will most likely
reveal itself when you scan for trouble codes. I hope some of these suggestions
help.