Re: sick baby (88 Blazer)
Look for a vacuum leak as suggested.
However, myself being the lazy POS I am, I'd look at the EGR valve first. Spark up your Blazer and make like a monkey and lay over the passenger fender. Stuff your pinky finger up the bottom side of the EGR valve and press up. Girly fingers aren't going to hack it. When an EGR valve opens at idle it's like one big-assed vacuum leak and the motor will piss and moan until you close it and the computer will try to compensate. If, while pushing up (and it's not easy, my cousin couldn't do it and he's a master mechanic grease monkey) there is no change then it's probably the EGR valve. Two bolts, twenty minutes, and a lot of cursing and you'll have it off. Once you get it off you can blow through it and see if it leaks.