I went on a 300 mile drive today in my wife's 98 V70, which I rarely drive. It began to run very roughly and seemed to lose power when accelerating up hills. This was on an interstate highway at speeds of 70-75mph. About 100 miles into the trip I was going up a hill and the engine seemed to be misfiring and bucking, at which time the check engine light came on. I continued on the trip and as long as I kept the speed at around 70 (rpm 2500 or below) and avoided sudden accelerations, it did OK.

I do not have a code reader. Any suggestions as to what the problem may be? Second question - is there a way to access the codes through some rudimentary flashing light sequence or will I have to get it hooked up to a code scanner at a shop? I was hoping to at least have the cause narrowed down before taking to the shop.

Thanks!