Wont start

Its the sensor in your transmission housing. By now you have probably figured out that by shaking the shifter and then trying again it may start. Also, turn the key forward, put your foot ont eh brake, shift it to Neutral, and try again. The car will start that way.

I have trouble with this and in two different mechanic shops and noone knows what the problem is. I cant get it started sometimes and than when it finally starts it will die 2 or 3 times going down the road before it acts right. When I am tring to start it sometime it will smoke. White smoke will come from the hose that runs to where the airfilter is. Someone told me to check the fuel injectors. Than someone told me to changefuel pump. I dont know what to do. It still backfires as well, and I have had 02 sensor changed and computer, ignition coils changed and it still does it. Help please.