XC90 Idle

daveb · Post by **daveb** » 14 Jul 2004, 11:17

With A/C on, 2004 XC90 idles at 800-850 and causes muffler rumble, esspecially in third seat. With A/C off idles at 650-700 and is as quite as a mouse.. Is this something that should be adjustable?

Post by **matthew1** » 14 Jul 2004, 11:40

Muffler rumble -- do you mean the tone of the idle is deeper? Or is the muffler vibrating against something?

The higher idle is necessary to run the AC compressor. It's a mechanical device that is literally run by the engine via the accessory (or 'serpantine') belt. The engine needs to run a bit stronger to turn the compressor's pulley. That's why you should turn AC off if you're drag racing -- it's an engine power vampire.

Guest · Post by **Guest** » 20 Sep 2005, 21:13

If it is a vibration that you are referring to, the vibration is more than likely harmonic vibration that begins at that rpm. This is a natural phenomena, like the "tuning fork" example. We dealt with harmonic vibrations on the MD90-XX that had the UDF engines that caused tremendous harmonic vibration on the tail of the airplane... In your case, I would check the mounting of the entire muffler system. Look that the condition of the muffler itself. Ensure that the exhaust system has plenty of clearance in the underside of the body tunnel. I have a 05 XC80 2.5T and noticed that muffler is hung by large rubber grommets, check those grommets. Also, the engine timing may be off, have a tech look at the idle rpm. Vibration is natural. All cars are designed with dampers (engine mounts) and the engine (crankshafts) themselves are balanced, etc.