I recently popped a few codes on my '2012 Volvo S60 T5' and there is a strange hissing sound coming from the car. I recorded the sound and uploaded it to youtube (link below).

The sound only start after the car is warm (about 30+ min of driving) and is only present at idle or very low RPM. Once i accelerate, the sound goes away. When the issue is happening, the car has a very slight misfire. I'm guessing these two issues are connected because there is no misfire if the sound is not happening.

https://www.youtube.com/watch?v=5lWa...ature=youtu.be

P0101 - mass or volume air flow A circuit range/performance
P0300 - random/multiple cylinder musfire dected
P0301 - Cylinder 1 misfire detected
P0302 - Cylinder 2 misfire detected

I plan to replace my plugs and coils seeing as it is getting close to that time, although i'm not sure if the hissing sound is related to the mass air flow sensor or it could be a different issue.

Any help would be appreciated!

 

the MAF is just a tube with a wire grid that measures the air volume. Hissing suggests a vacuum leak or an intake air leak from the turbo to the throttle body. Best to inspect lines and tubing for cracks, spray around with some carb cleaner to see if you can fine where air is getting sucked in, check out the vaccuum lines/pump going to the brake booster. An air leak can cause misfires and a lumpy idle and throw an odd lot of codes.

 

I thought a leak might be causing this sound. I was also thinking this because the noise seems to be happening when there is back pressure (letting off the throttle and drop in RPM).
The only thing that seems weird is that the sound doesn't happen until i have been been driving for a while. What would be causing the leak to only start after about 30+ mins?

 

For anyone reading this post having the same issue, it was the PCV valve (oil filter housing) that was causing the issue.

Here is a good youtube video on the steps to replace the part.