97 ford explorer sport trac problems

my worst problem first my trans wont take off in drive or first i have to shift into second then once im moving about 10 mph i can shift into drive and its fine i was told its an electronic problem can someone tell me what to do fix it i need to know the name of the part and where to buy one ty

my second problem is when i put the same vehicle into 4 wheel driver i get a loud poping sound every few seconds can someone help me with this