Volvo: 96 Volvo 850 glt fault code(s) P0300, obd 2 scanner, volvo 850 glt

Question
I just bought a 1996 Volvo 850 GLT 2.4 non turbo and noticed while at about 60-65mph, on cruise control, that the car surges or jerks(sometimes vilolently).
The RPM will increase about 1000rpms and then return to normal (about 2500 @ cruise). I thought at first that the transmission was acting up because it appears the it is downshifting.
The symptoms are similar to a throttle position sensor going bad.
I hooked up a OBD-2 scanner to it today and found the codes P0300,P0301 through P03005. All this tells me is that there is a missfire going on in all the cylinders but, not what is causing it. Have you ever come accross this before?

Answer
Hello Erik! That can be caused by a number of things. However, I would check the distributor cap, rotor and ignition wires. They may be corroded. Also replace the plugs. A vacuum leak could also cause that problem. Check all the vacuum lines to bake sure they ar ok.

Jimmy