I've had a quick search on here and found a useful quote from Honest John:

'Intermittent power loss on TDI 90s and 110s may be due to one of the following:- sticking turbo due to dirty oil; dirty or faulty mass airflow sensor; exhaust gas recirculation solenoid valve sticking open; wastegate valve actuator rod sticking; faulty throttle switches; faulty temperature sensor; loose or leaking brake servo pipe or turbo boost pipe from fuel pump to turbo; faulty ECU'

Not specifically related to a Skoda I know, but as the engine is used in the Octavia, I thought someone may have some additional comments:

My parents have an X-reg Golf TDI 90 auto which suffered reduced power a couple of times in the last week.

At the VW dealer today they hooked up the diagnostic computer and the guy said it had flagged up a turbo problem; the turbo had apparently overboosted at some point and had therefore prevented further boost. Would that be covered under any of the Honest John list? The car was purchased used from a VW dealer last year with only about 13000 miles on the clock and the warranty runs out in 2 days!

The flag has been deleted so it should be OK until the next time; but it is rather dangerous as you can't guarantee that you'll have the power to perform an overtake at any time.

I've suggested that they try to get the MAF sensor replaced under the remainder of the warranty. Is there anything else that should be looked at?

Sounds like an air mass metre to me, they are about