hey guys ive got a 98 blazer , (did have a 95 til it ate 5 new cfi units)anyways, i just got it and am trying to fix a laundry list of problems with it, this problem im working on is it idles kinda rough when in gear with the brake applied at a stop light or sumn sittin around 550rpm or so but as soon as i go and give it a bit of gas and drive off, its as smooth as can be, even if i hold the brake and just give the slightest gas at all it will smooth out(also the oil pressure drop to about 20, but ive readon here thats normal) so any advice on where i should start would help, only code i have is p0446 evap vent code(which i would like opinions on too), we have checked some or most of the vacuum lines and appear to be ok, and i have got new plugs cap and button to put on it , but i dont think that is really it , i just got those because i think it needs it

 

check the idle air control valve and your air filter, 550 rpm is a little low mine idles around 650 - 700

 

check the hose from the air inlet tube from the air filter to the valve cover i was having a similar problem but my code was evap low pressuer sensor code my hose had a rip in it replaced the hose idles smooth and no code

 

You could have a leaking booster.

 

thanks guys, i checked the iac and a few other things and they all checked, so i decided to throw parts at it, plugs wires cap and button, and so far so good, its smoothed out, now i got a evap code, but ill start a new thread