I bought a 2013 T3 TDI with almost 100k miles on it recently. Having owned a few TDIs I know intake manifold clogging is prevalent when you combine the inevitable oil in the intake with the soot from EGR flow.
Pulled the intake horn off my rig and it was no different
The first one actually looks a little worse than it is.. but, it's bad. 1/8 to 1/4" of nastiness all around. I'd guess it's less thick further into the manifold where velocities are higher, but there's no way it isn't impacting performance, and definitely needs to be fixed. I thoroughly cleaned the intake horn, EGR nozzle, and intake swirl flapper control, and scraped as much out of the first bend of the IM as I could. I'm sure there's still a ton back there.
I've already ordered a spare manifold from germany and the goal is to find a way to clean it without destroying it, to be swapped on later. At the same time I'll rig up something similar to what they do on BMWs using walnut shells to clean their intake ports on the direct injection engines.
I suspect walnuts will be too harsh for the manifold itself, however. At the moment the plan is to build a 360 degree soda blasting nozzle out of nylon tubing and some fittings from home depot..
I've tried chemical treatments in the past on aluminum manifolds and unless they are baked or use the extremely harsh chemical tanks at old-school machine shops they don't end up fully cleaned. Caking to this extent basically laughs at the "put it in a bucket of purple power overnight" advice. That didn't even work on the GM truck manifold I had to clean. Ultrasonic is nice but in the past shops haven't wanted to deal with how thoroughly a TDI manifold will ruin their fluid.
Anyway, curious whether anyone has dealt with this before, or has any thoughts on ways to get the manifold cleaned.
Also, just for entertainment, here is what the often-clogged 99-03 VW ALH engine can end up looking like:
I've personally worked on a couple that my thumb wouldn't fit into the remaining path available for airflow.
If anyone else wants to go down a similar path the intake manifold part number is 059129711CF and not too expensive used on ebay from europe. New, roughly $450. And you'll still need to clean the intake ports on the head. I'll likely end up keeping my original to clean and have on the shelf as a spare to be swapped on later. Who knows, if I can figure out how to clean them I might import a few and start a cleaning service.