For anyone that's interested, I used the 'Bent Vacuum Hose' method to clean my intake manifold out, as I couldn't get it off the car. I don't see this documented anywhere so just in case you find yourself with the same issue....
I couldn't get the manifold off the engine block as the bolts were obscured by the EGR heat exchanger, and I couldn't get that off either as the exchanger exhaust allen bolts were stuck fast and rusty. Many garages only offer to replace the manifold and not clean it. The 'belching propane fire' method is a step too far for many garages.
*If* you can get the intake manifold off the block then use the 'propane and air compressor' method to burn all the carbon out. There are many howto videos on YT. You'll end up with a cleaner manifold this way, as opposed to the method below. If you can't get the manifold off, you'll have to clean it in place.
Start by wearing gloves. EGR carbon seems to be a mixture of un-burnt diesel, oil and carbon. It stains, sticks and stinks.
You'll need to remove the EGR to gain access to the intake manifold. This is well documented on YT and forums. I needed propane heat on the EGR exhaust allen bolts to get them to budge. A long thin neck torch helps here as you'll be poking it below the EGR and there's not much room. A plumbers heat shield matt is also necessary to prevent melting rubber hoses. Without heat you'll run the risk of stripping the EGR exhaust bolts and that adds a whole new level of difficulty.
Once you have the EGR valve off, you can just poke at the carbon with your implement of choice. An awl or old screwdriver. Don't soak it in liquid. There are vacuum diaphragms on it.
If your intake and EGR look like the picture below, it's time to give them a clean. The parts below have 185k miles on them.
With the intake manifold attached to the engine block, you'll have to reach inside and scrape it out without allowing debris to fall down and block the intake valves. The problem here is that the manifold is a curved airway, and it splits into four smaller curved airways.
1) A vacuum cleaner with a remote hose and,
2) A one gallon plastic bendable fuel filler hose. The kind that comes with plastic fuel cans that can be bent into shape. This is just the right size to fit into the smaller passageways of the intake manifold.
Tape the filler pipe to the vacuum hose to make a seal. Cut the end to size if needed.
With the vacuum on *gently* poke at the carbon build up in the manifold. The smaller chunks of carbon will end up in the vacuum cleaner and the large chunks will just stick to the hose end; pull these out. When you need to get into a different passageway on the manifold, pull the hose out and bend it to shape. This allows you to get in at almost right angles. The trick to using the end flexi-pipe is that it's flexible enough to hold an initial shape to get you into the correct manifold passageway, but rigid enough once you're in to hold shape wihtout crumpling while you dig out the carbon. A bent copper pipe wouldn't work, it would get stuck at the first bend.
It's also worth considering an EGR disable while the EGR is out, but it's optional. It's just a blanking plate. They're cheap enough though so just order ahead of time if you want to alter exhaust recirculation.
Hope this helps.