I have a 98 T5M with 73K miles and recently had a similar problem.
Actually, twice. First case it set off a code that related to the
turbo overboost relay (or similar). That seemed like it was not
really the problem. Second time it stalled at a light and no codes
were set. I have no real fix to offer, but I'll list my symptoms
in case it seems familiar.

I had problems restarting the car both times. Took several tries
and I had to rev the engine high to "clear" it.

In both cases I had gone about a mile and the car was cold but not
very cold (weather was maybe 45 degrees).

Today I noticed that while parked and in neutral I could not rev the
car to 1500 RPM. It would over or under shoot. When I let off the
gas (with the engine between 1800 and 2400 RPM) the tacometer would fall
quickly and often down to 500 RPM where it would stumble and then pull
back to normal idle (if the car had been cold I bet it would have
stalled). This was repeatable. I then cleaned the throttle, disconnected
and reconnected two electrical connectors near the throttle and one
at a relay right above the fan (a vacuum line from it leads to the
throttle area). After this, I could rev the engine to 1500 RPM and
it would hold and when I took my foot off the gas it came back slowly
to idle (never over shooting it down to 500 RPM). Soooo, I'm thinking
something with the idle control mechanisms is at fault. I doubt I
actually fixed anything and I'm waiting to see if the problem returns.