Rough idle - no codes

[jmil1974]

On my past LSs, this is usually dirty injectors, dirty MAF, worn motor mounts, a PCM update, or even occasionally fuel filter and/or fuel sender. Any other things y'all have experienced personally? Drives perfect otherwise, besides the DoD piggishness and MPGs are where they should be. Only happens in gear (when the idle is lower) and I replaced the spark plugs with no change. 2012 with 95k miles.

 

[Geotrash]

On my past LSs, this is usually dirty injectors, dirty MAF, worn motor mounts, a PCM update, or even occasionally fuel filter and/or fuel sender. Any other things y'all have experienced personally? Drives perfect otherwise, besides the DoD piggishness and MPGs are where they should be. Only happens in gear (when the idle is lower) and I replaced the spark plugs with no change. 2012 with 95k miles.

Did you replace the plug wires too?

 

[BG1988]

On my past LSs, this is usually dirty injectors, dirty MAF, worn motor mounts, a PCM update, or even occasionally fuel filter and/or fuel sender. Any other things y'all have experienced personally? Drives perfect otherwise, besides the DoD piggishness and MPGs are where they should be. Only happens in gear (when the idle is lower) and I replaced the spark plugs with no change. 2012 with 95k miles.

i'd give Royal Purple a try

I'm testing it in my rig it seems to be doing it's job and is far more effective.. but time will only tell i'm at lest seeing new lows on the fuel trims +3-5 on the LTFT before I was seeing +15-17 on average it's averaging around +8-10 now

i'm going to put in a second can tomorrow and a long drive on the 21st 150 miles ish

lucas did get it to around +12 on average that was almost half of a gallon of injector cleaner and is no longer doing anything

 

[swathdiver]

On my past LSs, this is usually dirty injectors, dirty MAF, worn motor mounts, a PCM update, or even occasionally fuel filter and/or fuel sender. Any other things y'all have experienced personally? Drives perfect otherwise, besides the DoD piggishness and MPGs are where they should be. Only happens in gear (when the idle is lower) and I replaced the spark plugs with no change. 2012 with 95k miles.

High Long Term Fuel Trims, LTFTs, caused by exhaust manifold or intake manifold leaks.

 

[91RS]

Engine mounts.

 

[Fless]

As long as we're lobbing suggestions: dirty throttle body.

 

[SNES Avalanche]

Welcome to the club!

 

[jmil1974]

Did you replace the plug wires too?

I didn't since they look good (no arcing), feel good, and no codes. I may sling some on there though, just to rule it out, even though there was no change before/after.

 

[avalonandl]

How many miles on the plugs? When I bought my Denali it had 134k miles. One look at plug # 1 and I knew they were the OE plugs. Vehicle ran fine but idle was a little rough. New plugs and wires fixed that. Also i cleaned the throttle body and that helped.

These 900's have lousy engine mounts also.