I have a '98 Peugeot 406 with a 2.1TD engine, which seems to work fine, but
there is a slight niggle with it. When I first start the car in the morning,
a few seconds after it starts I can hear and feel the engine kind of
stalling but it never does. The idling speed drops from the about 800 to 750
and then back up to 800 - all within a second. After that it idles
perfectly. Am I right to assume it does some sort of idle speed adjustment
or something? Now the other problem I have, which may or may not be related
to the one above, is when I drive the car at high speeds... say over
90mph... I can again feel this.. shuddering, like someone has lifted the
foot off the accelerator for a second. Or an even better description - a
side wind! I never paid much attention to it until recently I was cruising
on the motorway at just over 90mph and again felt this shudder, and when I
eased of the accelerator, there was a "clunk" from the car somewhere and
engine simply stalled with the orange diagnostics light on... I pulled over
to hard shoulder, switched the ignition off and then back on - it started
without a hitch and I got home without any further troubles. But I can still
feel this when starting the car from cold (although it doesn't always
happen).

I bought the car at 74k on the clock and has now done 86k. It had this
problem from the beginning. Its glow plugs have been replaced at around 66k
along with the timing belt and water pump. Last service was at 81k with an
oil change, oil filter change and air filter change. It's due for another
service soon.

I am not a petrol head (or a diesel head for that matter!) but could the
above problem be related to too much air or fuel being fed into the engine
causing it to "splutter"? Or could it be something else?

The car otherwise runs fine and starts first time every time.

Any input appreciated ! :)

Thanks

Alex