Service engine light came on yesterday. Car started running rough and seemed like it would die when pulling up to a stop. While stopped the light would stay solid, but while driving it would flash. Temp stayed normal and no other lights were on. Hooked up a scanner and it said random sparkplug misfire. In talking with people we have been told it could be a coil pack and also the computer. How do we know if it is computer w/o putting money out for parts that may not be defective? Funds are very limited and we are trying to repair effectively and as frugally as possible.