R50 dying in shallow water

[qatarR50]

Hi, first and foremost, I'm no mechanical expert by a long chalk. However I'm not stupid either, and I'm hoping someone here recognises the symptoms I am experiencing.
I have 2002 3.5L V6 petrol R50, had it about 2 months. Generally I love the model and living in a very hot, dry, desert country the car is pretty competent for most offroad driving here. Typically deep sand and sand/rock surfaces, and it's already proven itself on dune climbs, etc.
But when I encounter even shallow water, say at the beach, the car just dies. Water two thirds or half way to the hubs, just crawling between sand banks at low tide.
It's happened twice and symptoms are same or similar each time - engine cuts out with no warning (no spluttering or progressive loss of power - revs just drop to zero, engine stops). It will turn over and start again immediately, but won't *move*, i.e., as soon as I need any power it cuts out again.
When pulled out of the water or sludge it will spend a few minutes being started and immediately stopping before eventually it will continue to run and generate power at lower revs, and a bit spluttery & rough.
Last time it happened, in a calf depth seaweed sludge, I was pulled out by another car and eventually got moving again as described above but at about 2500 rpm the revs were "bouncing" down & up as if it was hitting a rev limiter or something. So I could drive home but not with engine revs > 2500.
This continued for a couple of hours (even stationary) until I guess "something" had dried out.
Does anyone recognise these symptoms in this model, and/or have any advice for me?
As a an automotive novice I have to say that I suspect either something electrical, or maybe more likely some sensor killing the engine because of either a sensor fault or real water ingress or breathing blockage.
Thanks in advance for anything.
Ged

[fleurys]

this 2500 rpm limit thing is typical of a bad maf... The original MAF on the 2001-2004 will all eventually fail.... looks like yours is up... any code or check engine >?