Swirl flaps - are they worth it?

[TheMatador]

Anyone got any thoughts on the value of the swirl flaps in the V6 and V8 tdi engines?

Official documentation states "They enable the airflow to be adjusted to suit engine speed and load. Not only additional power and torque result, but also lower fuel consumption and emissions."

They seem very problematic though and expensive to fix (over £2000 to replace both sides on the V6). There's a lot on the BMW forums about completely removing them on the 2.0d and 3.0d engines with, arguably, little or no effect on performance. - see attached technical docs for how they work.

They are basically on-off valves on one of the two inlet runners on each cylinder. Possible scenarios might be:

1. Mechanism wears or gets a bit impaired e.g. linkage is worn giving "lower limit" error - valves still work though - no noticeable effect
2. Motor is faulty - valves don't operate - loss of power above 1250 rpm because spiral runner is blocked
3. Valves break off and knacker the cylinders, EGR valve and turbo

Questions in my mind are:
1. Why does problem 1 warrant the engine management light coming on?
2. Are they worth the money? Any efficiency savings are wiped out by a £2000 bill after 80k for six bits of plastic and two motors
2b. Ditto for problem 3 - a very big bill again!
3. Why do you have to change the whole thing at once - they're only on/off valves
4. Is there any way to put an inhibit on the lower limit error or change the tolerance to stop the light coming on?