so my check engine light has been on for a while mainly for the fact that i have no exhaust so it was all just emission codes coming through. well what i didn't realize is when they had to replace the stock motor at 37100 miles because the guy before me raced the truck, one of the delaersships techs apparently forgot to tighten my spark plugs down. so today we go through the check engines again due to the fact that my truck had been idling at about 4-500 rpm and got to thinking what it could be. we thought it might be the throttle body cause i guess they've been known to go bad on the trailblazers but we checked that and it was relatively clean so my next thought was just a bad spark plug. so i pulled out the first chamber and it was completly black cause the exhaut was flowing back in and igniting in the spark plug chamber for lack of better words. so i went through and replaced them all because the old ones had worn quickly because of it and then i called the dealership justout of curiosity to see what they might charge to diagnose and fix a problem like that. i think it upwards of like 2-300 for parts and labor. i spent thirty bucks and forty five minutes doing it and 15 of that was waiting on the spark plugs to get there. so just as a note to anybody if you have a problem wit ha low idle speed go to the spark plugs first.