2008 suburban 5.3
dod/afm delete
Brian tooley stage 1 truck cam
Ls6 blue springs

Currently idles at 625rpm both in gear and in park. Believe it or not the rough idle is more noticeable out of gear than in gear which is strange and out of the ordinary. Runs great above idle just has a rough shake at a idle.

Ive tried everything in my book of tricks and am stumped....
-new spark plugs
-new wires and even tried another set
-swapped 1 bank of coils at a time with another set i have
-cleaned maf
-cleaned throttle body
-swapped to another throttle body
-unplugged fuel injectors one at a time, cyl4 didnt seem to be quite as noticeable when killed. Replaced cylinder 4 injector with no change.
-cleaned out fuel rails and sprayed out top side of all injectors.
-installed updated square port pcv driver side valve cover (oil in intake rough idle GM tsb)
-inspected air intake tubes to make sure there wasnt any cracks or anything where the silencer pieces are moulded into the main tube, siliconed around the joints just in case.
-no misfires are being picked up at idle, no misfires even power braking it.

What else could i be missing?

 

Mild misfires can cause that...most tooners will disable misfire detection. It can feel worse without the load from the transmission/converter which tends to push it above the lower cylinder charges that result in combustion instability. Increasing the idle speed or enriching the idle fueling can damp out the roughness, but otherwise that's something you're stuck with if you have a bigger camshaft.

 

Doesn't the IAC add air when it's in gear?

 

It was turned off originally but ive turned misfire detection back on because it wasnt an issue with how small of a cam this is. It is not detecting any misfires.

Maybe i will bump idle up another 25-50rpm and see if that makes any difference.

 

Cracks the throttle blade in this case, this is dbw so no iac.

 

You can turn it back on, but misfire detection must be calibrated to the camshaft. Give the higher idle a shot, worst case play with the closed loop control to enrich idle a bit.

 

Appreciate the info!

 

What are the fuel trims showing?

 

If i remember right it was 2-3 on average it idle. I will up a log and confirm that though

 

At idle bank 1 and bank 2 bounce between 0 and -3 for short term fuel trims
Bank 1 long term is +5
Bank 2 long term is +3

After seeing these do you still think richening it up may help?