Just did our 2013 XC90 D5 today. The polymer used for the intake manifold appears to be very robust, certainly hot (ish, say 75 C) water would not bother it.
As for me, I scraped out as much crap as I could, and used a combination of oven cleaner, and then degreaser (with various brushes), then a soak using some turps, then some more degreaser. In the end it was reasonable, still a little gunk left inside it, but realistically good enough. The system has clearly been designed to run with some degree of crap in it, so some stubborn minor traces of gunk left on the inner surfaces wont bother it. I also cleaned out the EGR system, that was quite a job, all doable, just time consuming. Here are a few photo's of what the system looked like before I cleaned it, and believe it or not it ran OK, just much better now!
This first image was of the main inlet to the manifold.
![Image description](https://cdn.ozvolvo.org/assets/files/2024-05-11/1715430115-960952-image.png)
Here is (believe it or not….) a picture of a section of the swirl flap with a thick layer of crap… BTW, the swirl flaps are easy to change, once you have gained access.
![Image description](https://cdn.ozvolvo.org/assets/files/2024-05-11/1715430230-963568-image.png)
And here is how the inside of the outlet end of the EGR looked like..
![Image description](https://cdn.ozvolvo.org/assets/files/2024-05-11/1715430382-630759-image.png)
So as you can see there was a slight buildup of muck.
What I suggest is that worrying out the final 0.003 mm thickness on the inner surface of these parts is not going to affect the performance one bit. I would say however that all loose material, and obvious gunk should be removed.
As for the swirl flaps, I choose to replace them on this occasion, it may be OK to clean them, and then re-install. I purchased my parts from Skandix. IPD and FCP Euro don't seem to stock the Diesel bits. There are a few good YouTube videos that show the process.
It is also important to remove the injectors carefully. Any damage caused by careless or overly forceful removal may result in injector damage, which will then necessitate expensive replacement and subsequent injector coding.. I also cleaned the outer part of the injector barrel and coated them with a thin film of a nickel based anti-seize prior to re-installation. If they are stuck, then perhaps try some penetrating type hydrocarbon.
I also modified the end of a vacuum cleaner so that it had an approx 15mm poly tube (250 mm long) that I could insert into the inlets / injector holes etc to suck as much crap out.
This job is definitely doable, but requires care, patience, preparation, and above all, lots of disposable nitrile gloves, it is a surprisingly messy job..
Good luck with it.