Surging sound at idle but RPM's do not Move

APRIL LOUISE

MEMBER
2005 VOLVO XC90
2.5L
5 CYL
TURBO
2WD
AUTOMATIC
148,000 MILES

My car started idling weird within the last two months. What’s happening is that when I am stopped the idle is somewhat rough, but mostly, it is making a sound like the engine is revving up and down. The RPM's do not change, even with the surging sound it remains at about 700 RPM's during idle. It is exaggerated when using heat/AC. Things I have had replaced so far, since I bought the vehicle back in June of this year:

-PVC system
-O2 sensor bank 1
-Water pump/timing belt
-Air filter
-Fuel filter
-Battery

Services I have had done since June:

-Fuel system cleaning
-Oil change
-Transmission flush
-Cleaning of MAF
-Tune up

2 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

Based on your description, the idle isn't the issue since it remains at 700 RPM's. Since it gets worse when you use the A/C or heater, I'm questioning if it is a noise from the alternator because of the added load placed on it or there is an accessory drive belt issue.

Is it possible for you to record the sound and upload it for me to hear? Also, does it change if you turn the lights on and off?

I attached a pic of the accessory drive belt below. I highlighted the automatic tensioner. If that is getting weak, it can allow the belt to loosen. Check to make sure the belt is tight. Also, and don't laugh, when it is making the noise, pour a small amount of water on the belt. If it changes or the noise or goes away, we know it is a belt related issue.

Let me know if you can record it and upload it. That would really help.

Take care.

Joe

Image (Click to make bigger)