I have a '99 Alero, 3.4L 6cyl; "SERVICE ENGINE SOON" light came on about a week or so ago; looked in the manual and performed the troubleshooting items suggested, light remained on. Before I had a chance to take to a mechanic for check, was on the freeway when car started to lose power, choke, sputter, and "SERVICE ENGINE SOON" light began flashing. Had car towed home, now when I try to start it = very rough choking noise. Should I think plugs, wires? Friend tells me maybe cracked block. I DON'T THINK SO???????? Thx, Karen