Are you sure your timing belt is ok?
My sons concorde did that, Then eventually called up the cam sensor. The sensors are basically prox sensors the pulley/gear have a gap in them both, the crank and the cam(Iknow there are two cams) The idea is both of these sense the gap in the gear at the same time indicating your timing belt is ok.
We had to change the belt. Not a terrible job. There are marks on the gear to line everything up. Hopefully yours is something else. But your belt maybe streching/wearing.
Good luck