'98 Dodge Caravan Tranny

A friend of mine called me today with some problems he is having with his van. He said that it was leaking oil real bad, but they had a guy fix that. The guy said it was the seal around the timing chain cover, while putting it back together the dumbass guessed what the timing was, idiot. So now it is knocking and backfring and not able to idle. But the bigger problem is, the van will go into reverse, but not into any forward gear. It is their only vehicle, and they called me asking me to fix it, unfortunately I know nothing about auotragic transmissions.. Their friend said it might be the solenoid. Any suggestions?