It won't be the PCV causing that
Will it rev any higher in neutral or park? Will the car actually move or try to pull off under its own power? Are there any lights flashing on the dash, does the gear indication display the correct gear?
Impossible to say for sure, certainly not without a lot more info and a much better description. Diagnostics needed, hopefully the RAC man will at least get you some fault codes and get you home or to a place of repair, as I doubt he'll be fixing it at the roadside
Does sound Gearbox related though