please help me figure out this missfiring

[josueh95]

about a month ago i did a WOT pull and right after my tahoe started missfiring pretty bad i let off the gas and it would rev up on its own a couple times..while i was slowing down coming to a stop it would almost die out..i got home and it kept doing it but less intense..the next day i installed my BB tuned PCM that arrived and i did not get that problem at all truck ran perfect! days later i begin to feel the truck shaking at random times that im coming to a stop and im at idle..it missfires for about a minute and then goes back to normal..i also noticed that sometimes if i shift into neutral or Park the missfiring goes away and sometimes it doesnt...i replaced my Intake gaskets and it felt smoother but did not fix the issue..i checked my spark plugs and all four on the passenger side had some carbon coating on them and the drivers side did not..the O2 sensor on the passenger side is new and now so are the spark plugs and cables...still have some missfiring!!! i can somewhat hear that i might have a vacume leak as i can hear a whistling sound coming from the intake manifold but cannot find the location of it..i do not have a scan tool or testers..i sprayed carb cleaner all over and no changes in idles anywhere so where are some vacume lines that i can check where it might have a leak and any other suggestion would be apreciated..my gas milage has also dropped alot which is why i need to get this fixed

 

[Atomic]

Having access to a scanner would be very useful...at least then you could narrow down what bank it is. Try the standard compression and leakdown tests.

 

[nuc_meltdown]

My 2000 Silverado has the EGR tube that runs to the front passenger side of the intake. I didn't get it seated properly and it caused some of the issues you described. It was a pia to get flush. Might check that.

 

[josueh95]

huuumm might have to check that out soon! thanks i apreciate it

 

[livingez_123]

weak coil pack?

 

[josueh95]

honestly i feel like i can hear a vacume leak in there but i cant find it anywhere! ive sprayed carb cleaner everywhere and nothing...replaced plugs cables and manifold gaskets and it got alot better bt still have some missfiring at random...also my purge selonoid valve ontop of the intake is all loose even with the bolt tightened down is this normal?

 

[livingez_123]

Have you done a throttle relearn? you have the 5.3?

 

[josueh95]

yea i have the 5.3 bt i dnt think i need a throttle relearn because my throttle body is a cable driven not electronic

 

[livingez_123]

it still wouldn't hurt, but what it's doing is resting the TPS. the ECM still controls idle the cable just opens it. the TB has it's own idle control, but if it was moved or bumped.......it wouldn't hurt to try it. cheap fix. My 6.0 had a very low idle issue after changing the CIA and cleaning the TB. Did a relearn and all is good.

 

[harveje]

kind of dangerous " Do at your own Risk" you can use ether or raw propane to try to locate the leak. I have a small propane bottle with an adapter and valve that goes to a 1/4 rubber hose I use, sometimes. I'm wanting to build a smoke machine in the near future.