One of the multiblocks was already soldered up when I got the car but after loads of issues:
###please add to this list if anyone has more errors accountable to these connector blocks########
...they are the ones I am confident were caused by dodgy connections in the multiblocks.
Still getting Lambda sensor plausibility errors, as I haven't soldered up the connectors by the radiator!
I decided to solder the other block my self. Heatshrink is great - use it!
I removed each wire from the block one at a time with the male/female connector still attached, then reconnected (not forgetting to thread the heatshrink tube on first) - I used a hand held butane torch (because that's what I had - no soldering iron) and lots of fluxed solder, making sure to use enough heat to make the solder flow throughout the connection, whilst being very careful not to set fire to anything behind what you're soldering! I have a jewellers charcoal soldering block for that but a stone or maybe a block of pretend coal from a gas fire would do.
_best tips for a soldering beginner are, clean off all grease, and solder will always flow towards the heat._
If I was using a soldering iron (probably a lot easier- cut the connectors off each wire and twist the wires together - then solder.
Try and keep all you're solder points low profile so you don't have trouble getting the heatshrink tube over them when you're done(like I did!)
Other tips- cover the wing and battery if you're leaning over it so you don't scratch/damage anything.
Take regular breaks cause the back of you're knees will be knackered from leaning over the engine bay - took me over 2 hours and I was sore as hell!
Let us know how it goes will you?