Just purchased this vehicle off a friend. Told me needs a little work, no problem. After doing all the paperwork took it for a little drive, vehicle sputters like there is no tomorrow. Feels like a misfire. Brought it to my garage, put a new cap, rotor, wires and plugs. Still doing the same thing and now the RPMs at an idle sometimes surge but rare. I am at a little bit of a loss. Any ideas?