94 850 turbo engine problem

My 94 850 turbo wagon (128,000 mi) had an engine problem twice recently, a
day apart, during easy suburban driving in moderate temperature. In both
cases it happened like this:

- I felt the power drop, then come back, a few times.

- Then the power dropped until the engine would only idle, a bit slower than
normal and a bit rough.

- Pressing down on the accelerator had no effect at all on the engine; it
continued to idle slowly and roughly.

- After several seconds, maybe a minute, pressing the accelerator had a
little effect increasing the rpm, then a few seconds later full response and
power were back.

Has anyone heard of something like this?

Thanks,

Mick Ruthven