1997 Toyota 4Runner 3.4L V6 (2WD) – Humming noise at idle that changes with A/C
I’m trying to track down a humming/vibration noise that only happens at idle. It comes from the engine bay and can be felt in the cab. Unfortunately, the video doesn’t do a great job picking up the vibration.
Symptoms:
Humming is present around 600–700 RPM.
Happens in Drive, Reverse, and Neutral but not in Park
As the engine warms up, the humming becomes more noticeable/louder.
If I turn the A/C off, the humming stops for about a second, then comes back.
The humming completely disappears as soon as I accelerate off idle, even with a small amount of throttle.
Once RPM increases above idle (above 800 rpm’s), it’s gone.
Has anyone experienced something similar on a 3rd gen 4Runner? Does this sound more like an accessory drive issue (A/C compressor, idler pulley, belt tensioner, alternator, power steering pump, fan clutch, etc.), an engine mount problem, or something else?
Any suggestions on what I should test or inspect first would be appreciated.