Hi All
I have Tahoe 2009 LT 2WD. My truck has 281,000 miles on it. I purchased this truck 5 months ago.

Since 2 months I am trying to figure out the rough idle on it while AC is on only & rpm goes up and down from 500-700 with vibration(when vehicle slows down) from cabin or under the hood not sure. (it stop fluctuating when I turn off the ac)
I also noticed the vibration like buzzing sound at 68 mph----(110 km/h).
Someone just frightened me yesterday that this is due to weak engine & that's the reason before going to mechanic I wanna ask your opinion.

I also changed my spark plugs 2 months ago.

Regards

 

Throttle body clean ? May need it with those miles if it's ever been done.

 

Our 2005 Yukon has a compressor driven by its own belt (and own tensioner), separate from the main engine serpentine belt. I think I'd pull that AC belt and spin the AC tensioner pulley by hand and listen/feel for issues there.

We had issues with factory AC compressor slugging and breaking AC belts on ours, fixed by replacing the compressor, maybe 8 years ago.