Hey guys. I have on 05 sierra 5.3 with K&N 77 series, flowmaster 40s, and an 87 octane Predator tune. It was idling a little rough, so i went to Oreilly's and the guy sold me a can of sea foam. Long story short he told me wrong and I didnt read the directions, so I poured it in with the engine off and it all flooded the left rear cylinder.I pulled all the plugs to drain it then replaced the plugs with NGK's and new MSD wires. Now the idle in drive is worse, its annoying when your at idle but the truck runs fine. Any help is really appreciated.

 

Dirty MAS?

 

as in its not missing off idle? if its only missing at idle i'd check for a vacuum leak.

 

Thanks guys, chevy112488 that makes sense considering i took off the vacuum line for the seafoam. Ill check that tomorrow morning. Also, its throwing a random misfire code. It only comes back on after it idles in gear for a while.

 

Ok, so i took a look at the vacuum line and there is no obvious leak. I did hear a "pulsing" hiss, it could have been a leak but i couldnt find it exactly. It seems to idle perfect after I take the hose off and it releases the pressure, then when i start it back up it it idles good for about 15 seconds. The code its throwing must be from the vacuum seal, I disconnected the hose while it was running and my check engine light came on right away. I really appreciate the help guys, this shouldnt be this difficult for me.