Became the proud owner of a beautiful one owner 2004 V70 2.5T 3 months ago. 66000 miles and all is well, but one thing. With the A/C on and at a stop light with the transmission in D there is a noticeable load on the engine that kicks in / out. It sounds like the A/C compressor and causes the idle to drop and the engine vibrations increase significantly. If the compressor is off the idle is smooth. Any suggestions as to what may cause the idle to drop so much and cause vibrations when the compressor kicks in?

 

Hello, Check your motor mounts. If the compressor was dragging that much it would be talking to you. Kira

 

Could be a leak somewhere in your vacuum lines, as well. I was in your exact same situation last week, with a varying idle at stops with the a/c compressor on, but no other issues which might signal ETM troubles. Additionally, the air was blowing consistently and coldly out of the vents, which made me realize that the compressor itself was probably fine. After a bunch of troubleshooting, I found that my (ex) mechanic had failed to properly connect some of the PCV hoses. I secured them, tested to make sure that the leaks were gone, and re-started the car; with the a/c on, idle is now smooth and steady.

Hope this helps, as re-attaching some PCV lines is way cheaper than installing a new compressor.