Today, I spent the day removing and cleansing the intake assembly, including the doughnuts and all accessible ducting.

However, I am unsure how far I should go in cleaning the 4 plastic inlet manifold ducts that are part of the two plastic induction manifolds.

They are currently filthy, and I feel it would be strange to put in the effort to clean the intake assembly and throttle housing but neglect the inlet manifold.

On the other hand, I am worried about accidentally dislodging and dropping debris down the induction tubing. What would be the best course of action?

Click image to enlarge

Wow, that's an amazing amount of debris and oily deposits. Makes me think I should take a look at my own. What miles are on your car? It seems to be a common issue.

It was as expected.

I live in the middle of nowhere and never sit in traffic, stretch her legs every time I use her and yet she still fills up. Pushing 120k now and it’s never been cleaned, so not too bad.

The throttle body was ‘ok’ on initial inspection, but I could see the butterfly-flap cutting through very dry and sooty crud. Not wet, very dry soot, which couldn’t be doing it any good.

It’s something I’ve wanted to do for a few years. I’ve experienced hesitation and non-linear power delivery. Cleaning the MAF sensor has always made a huge difference so I hope (fingers crossed) this also helps in smoothness. 2012 4.4 TDV8 Westminster - Baltic Blue, Jet interior
1997 P38 2.5 DSE auto & 1998 P38 2.5 DT Manual
1988 Vogue 3.5 EFI - Manual, gone.
2004 Volvo C70 2.0T convertible, had since new.
2007 Mazda MX-5 2.0 Sport Roadster/Coupé, had since new.
2024 Mini Cooper S cabrio, JCW kit, 2.0, DCT auto

This is something I also want to do although there are no clues anything is wrong, ie no hesitation, lumpiness or rough running and mpg is really good. Mine is on 82000 miles, is it really difficult to remove the intake manifold?

It's not difficult, you just need to be really careful of plastic parts breaking, like plastic coolant pipes.

...I broke a pipe yesterday... not too horrendous though.

You're taking the inlet manifold off to clean, not the intake manifolds.

Click image to enlarge