I have a 1990, 2500 series chevy truck with a 350. Check engine light came on. Next morning hard to start and runs rough when cold (Its been in the 30-40 in Chicago at night). Truck runs great after it's warm. No trouble starting the remainder of the day. We had a few warmer nights (50s) and it started much better but still not right,

Sound like a sensor to me but if you had to guess what would you try first. I hate to drop 85 bucks on a scan unless neccesary.

Thanks,

Dan