Ok, i just bought this 95 blazer, it has 155k on it, heres a little info leading up to the now rough idle. First day i got it, died going down highway, turned out to be the spider injector, replaced it. While replacing the injector i noticed the main vac line from the intake was unhooked, hooked her back up. Finally drove her home from the side of the highway, never noticed if it was idling rough at this time because i was more focused on getting it home. Any way, take my car to oreillys, get some new plugs, wires appear to be pretty new so didnt replace. I put the new plugs in, clean the cold air filter, start her up and shes sounding pretty good, then as she got warmer i noticed the rough idle a little. It was reading service engine so i put my obdii scanner on, it says TP Sensor, EGR, and some tranny code in which i cant remember. So i replace the throttle position sensor, and the pcv valve, Still rough idle if not a little worse. Next day i hear snapping coming from the ignition coil, had a crack in the side of it, another trip to oreillys, got her replaced, still rough idle. Well now im almost clueless... Finally i check the IAC valve, its a little dirty, cleaned it up, put it back on and apparently somewhere in cleaning it totally destroyed it... Started it up and it was running 2500 rpm and not slowing down so bought a new one... Now back to normal rpm, now the idle is worse than ever. To make it clear, its almost like a vacuum leak idle if you know what i mean, but ive checked all the vac lines, and used a vac gauge and it was at 19 at idle... It doenst idle rough until its warm... But when its cold started and idling a little high you can hear the misses id say every couple of seconds or so... Any more ideas? Map sensor is ok, havent checked compression and don't want to have to lol, havent checked the rotor cap, supposedly it was replaced recently, fuel pressure is at 55. Temp running around 185. Any ideas anyone? I feel as if im over looking something small lol

 

Did you change the spark plug wires? Also what brand cap rotor plugs are you using?
These trucks are fussy about that, only like ac delco stuff

 

I hope you got a good deal on it.
You better check the EGR to make sure it's not stuck open a little. They can carbon up and act like a vacuum leak.
What type of ODBii scanner do you have? I have a '95 and I have not found one that will connect to it. So far I've been able to keep mine on the road with a little luck and lots of careful troubleshooting.