Do not know for sure...but I bet there is, even if it may or may not be direct. If you are in Acapulco maybe ask at concierge, or go to bus station...otherwise maybe try googling bus lines in Mexico and their routes. Good luck!!
We took a bus from Ixtapa to Acapulco. Originally, we wanted to travel from Acapulco to Manzanillo, which is south of Puerto Vallarta. After checking into Acapulco-Manzanillo, we decided it wouldn't work well. The bus ride was extremely long; I believe we had to pass over a mountain range. It was a few years ago so I can't remember all the details. The ride from Ixtapa to Acapulco was approximately 4 hours, and it was interesting. If we went to Puerto Vallarta, we would look into taking a bus to Manzanillo as we own a timeshare in Manzanillo.