I have a 1999 Punto 60S (old shape) which has been an excellent car during
the four years I've owned it.

It drives well and returns about 40mpg in the Winter and 45mpg in the
Summer.

Each year it has sailed through it's MOT with no problems but I notice that
each time the fast idle Lambda reading is only a borderline pass:

1.027 against a maximum allowable of 1.030 (the minimum is 0.970)

By my reckoning that's only a third of one percent inside the limit!

Other readings are very low:

HC:    2 (max allowed 200)
CO:    0.00 (max allowed 00.30)

The car has covered 42000 miles (last year it had covered 33000 and gave
very similar readings)

This all suggests to me the car is perhaps running a little 'richer' than
ideal.

A few years ago I worked with Vauxhalls and one of the 'tweaks' you could do
to lean off the mixture a little was to back off the throttle position
sensor a little so that the engine management system thought that you were
in less of a hurry!

Although it's a year to my next MOT I'd rather suss this one out well in
advance - I don't want a fail and then an expensive trial and error exercise
looking for the problem.  Because I've had no real problemsI don't know how
much local expertise there is around here when it comes to sorting out the
tricky stuff!

Anybody got any ideas?