I want to buy this volvo 240 for 300 but it only goes 35 so somethings wrong. Anyone got any idea why its going slow and if its worth it?

 

Could be many different things. I would start with a compression check. If you aren't familiar with how to do it or don't have the equipment, then take it to a mechanic. The compression check should tell if there are problems with the rings and/or valve train. If any of the cylinders check lower than the rest, then the engine will need some major work.

Does the engine idle rough? Is it running on all cylinders? While it is running, you can pull each spark plug wire one at a time to see if the idle changes. If you pull a wire and there is no change in idling, then that tells you that cylinder is not firing.