ok so I've spent all day trying to find an answer to my problem and just am dumbfounded. whenever i start my truck for the first time that day, worse more so when its cold and there condensation covering everything, it starts up fine and will run decent, not great, but decent till i get out of my neighborhood but when i really give it some gas to get on to the main roads it wants to bog down and sputter till i let off the gas, once i let go and ease back into it it goes but then my rpms are running in the range of 2000-2500 rpms. the thing that really has me tearing my hair out about it and confusing me because I've seen other threads with similar symptoms is after its up to operating temp it runs fine like nothing ever happened, even once i park it and come back to having let it cool down it runs fine. I'm just so lost with it being so intermittent I just have no clue where to start i checked around some of the vacuum lines thinking maybe the condensation was getting sucked in through them but I've replaced the ones that i found that were completely dry rotted and still nothing. please if somebody can help me out you'd be a life saver.

 

1st off have a sig with your vehicles particulars, year, make, model, mods etc or just state them please.

You have it posted in 2nd gen so I'll <gag> assume it's a '95 or later.

I cleaned my (aftermarket) air filter & it made a HUGE difference, as well as the MAF.
Could be your IAT (sensor in the intake just beyond the MAF) that's throwing off the comp & making the truck stumble. A vacuum leak can cause a plethora of issues. How are all the lines from the intake & to the ball or box in the fenderwell & from there to the HVAC controls?
Could be 02 sensor/s causing grief, any codes, have you gotten it read?
Plugged cat perhaps.

 

^^,+1, also, check your distributor cap and rotor for signs of arching.

 

I apologize it is a 2000 blazer 4x4 4 dr. No mods but I did just replace the heater core 2 weeks ago. I could be wrong but I don't believe it was doing this before I changed the heater core, it's hard to remember because I got really sick it took about 3 weeks to finish it. But one thing I'm gonna check but doubt it is the problem is I do believe I didn't get a vacuum connection back all the way together around the heater box. Also I was wrong on the rpms, I payed attention to them this morning they were at about 1800-2000 which is about 500 higher than normal. I also checked just a litte bit ago and couldn't see anything arching in the engine bay but I'm gonna check again in the morning since that's when it does have its issues. I'll post more here in the next day or two when I get that vacuum line hooked back up correctly.