Another rough idle and new codes...

[05YukonXL]

I can switch the scanner to 'metric' readings on the next run... assuming that goes to grams/sec reading.
.01 lbs/sec = 4.53592 g/sec
.02 lbs/sec = 9.07185 g/sec

 

[swathdiver]

Those long term fuel trims are way off. Yeah, something might be up with his MAP and MAF readings, hard for me to tell, don't know enough.

So what causes high trims? Too little fuel. What causes that? Bad or Lazy O2 sensors or the wrong ones, bad MAF sensor, intake gasket leaks (usually the other way around, too lean) but stranger things have happened.

So, how old are your oxygen sensors? If they have been changed, when and what brand was used? Any other sensors changed? Did you try tightening the 10 intake bolts?

 

[05YukonXL]

Those long term fuel trims are way off. Yeah, something might be up with his MAP and MAF readings, hard for me to tell, don't know enough.

So what causes high trims? Too little fuel. What causes that? Bad or Lazy O2 sensors or the wrong ones, bad MAF sensor, intake gasket leaks (usually the other way around, too lean) but stranger things have happened.

So, how old are your oxygen sensors? If they have been changed, when and what brand was used? Any other sensors changed? Did you try tightening the 10 intake bolts?

Thanks for the feedback. Interesting ... Got this truck second hand and to my knowledge no oxygen sensors have been changed during my ownership. Indeed the 174 and 171 codes are LEAN both banks. I have not tried tightening bolts ... but I can. (Only sensor I can think of that was changed was ABS speed sensor to help clean up some ABS/Stabilitrac dash warnings.)

 

[swathdiver]

Thanks for the feedback. Interesting ... Got this truck second hand and to my knowledge no oxygen sensors have been changed during my ownership. Indeed the 174 and 171 codes are LEAN both banks. I have not tried tightening bolts ... but I can. (Only sensor I can think of that was changed was ABS speed sensor to help clean up some ABS/Stabilitrac dash warnings.)

The consensus is to change the O2 sensors at 100K miles. Now if you do, use only GM OE:


Both numbers are on the same box. Sometimes one number is advertised at a lower cost than the other across the internet.

 

[05YukonXL]

The consensus is to change the O2 sensors at 100K miles. Now if you do, use only GM OE:
View attachment 396566

Both numbers are on the same box. Sometimes one number is advertised at a lower cost than the other across the internet.

Today's update:
1) Temps back up in the high 70's and the rough idle is much 'less rough'.

2) Looked at the four O2 sensors (didn't remove). The two UPSTREAM sensors have, at some point, been replaced and certainly look less weathered than the two downstream sensors that appear not to have been replaced, or at least not in a much longer time. Since both DOWNSTREAM looked weathered (maybe originals) I ordered a full set GM replacements ... Ironically, the GM BOX had DENSO branded sensors inside.

3) When I went to replace the sensors this evening I found the driver side DOWNSTREAM sensor was seized in place (you know the easiest one to access) - while the other three were easy to loosen. Will try again in the morning when I can move truck into better spot to get under it.

 

[petethepug]

Clean and/or consider replacing the MAF due to age and milage.

Just like the other recommended advice, use OEM GM only that has the security hologram on the box. Change your battery cables because they rot from the inside out. They starve the 5V can bus of voltage and cause gremlin codes to chase.

I suspected the rough idle in our past 08 YXL Denali was injectors @ 140k mi. I sold it for our 09 Escalade ESV with the same rough idle. Replaced with OEM injectors and o2 sensors and it’s smooth as butter at 170k miles.

I shopped all the sales and got the OEM GM parts on the cheap.

 

[05YukonXL]

Well then.. new O2s in, a few other tests and and a steady decline rather than improvements in the idle. Handed it over to my new mechanic. Compression on Cylinder 5 @40% lower than 3 and 7 at idle, better readings at high RPMS. Things pointing to bad lifter. More info in a couple days.