on my 06 s60R, to my disappointment, the car wouldn't run right. Started with a super high idle, and then drop super low almost to the point of dying. After awhile, the car would idle but would fluctuate bad, up and down, up and down. Well, that was 3 months ago and up until this morning, I've spent everyday since trying to figure out what's wrong. I even went as far as replacing the engine wiring harness thinking it was just a from old corroded wires. But this morning, I randomly decided to check something out after remembering something. What I remembered was while I was installing the IC, I broke one of the A/C lines. Not really caring about the A/C (as I have another 05 s60r with perfect A/C 
),vI decided to just remove all the lines to the A/C as well as the condenser (Also I later found out that's it's pretty much impossible to have the condenser there if installing the bigger IC AND the piping kit because even without the condenser there's barely any room). On top of that, to keep the A/C pump from accidentally running, I removed the relay from under the hood fusebox that was marked for the 'AC'. So, earlier today I decided to quickly skim over some electrical documentation I had from the earlier job of the wiring harness, and thought I came across some sort of connection between the AC relay and the throttle positioning function. Thinking this was not possible, I decided to give it a shot and throw the relay back in. And what do u know!!! The car started right up perfectly, idles perfectly, and runs flawless like nothing ever happened. 3 months to find out it was a fuse. I was in a slump over this. Im better now tho 
. Anyways, thought I'd share this experience in the chance it might help someone else out who's out pulling their hair. Best wishes to you all and your families!!