Your car uses SPI - single point injection.

The unit is in very repsect like a traditional carb body, except that the
normal jets are replaced by a single pulsed jet in the middle of the body.

Your mechanic needs to:

With engine OFF
1) remove the top of the air filter cover allowing him to see down inside
the injection throttle body.
2) manually operate the throttle plate checking for smooth free rotation.
(disconnect the throttle cable first)
3) check for smooth throttle cable travel and return (don't reconnect yet)

With engine running

1a) operate manually the throttle plate whilst looking inside the throttle
body.  The fuel injection/mist is readily visible and should respond to the
manipulation.
2a) visibly check the idle control solenoid (acts on throttle plate shaft
linkage).  Should retract when the revs are manually lifted.  Should extend
if the car revs are slowed by a) dragging the clutch in gear b) restricting
the air intake.

Stop Engine

1) reconnect throttle cable

Start Engine

1) Repeat 2a) above.

If all looks OK and problem still persits then the ECU possibly needs
resetting/conditioning.

The ECU is adaptive and can memorise events/conditions/driving styles.

I believe, if I remember correctly the following procedure will retrain the
ECU (suggest you try your own internet searches to confirm).

a) disconnect battery for 15 mins
b) start engine and allow to warm up at idle till fan cuts in (about 15
mins)
c) rev ingine to 3000rpm and hold for 3 to 5 minutes
d) allow engine to idlel for 5 mintutes
e) take car for a 'normal drive'

If in b) c) or d) the car performs irratically then there is another problem
lurking.

Additional info I have from my files is:

Fuel Injection System
---------------------
 Bosch Mono-Jetronic (SPI) Single Point Injection System - A2.2
  (data provided by Bosch UK)
 Air Temperature Sensor: 2.23K ohms at 25 deg.C. (approx. measured)
                         1.91K ohms at 31 deg.C. (approx. measured)(finger
temp)
                         (two outside connector pins)
 Water Temp.     Sensor: 2.43K ohms at 24 deg.C.    (approx. measured)
                           329 ohms at 75/80 deg.C. (approx. measured)

Digiplex 2 Pinout
-----------------

 1 - ground to retard ignition by 3 degrees
 2 - ground to retard ignition by 6 degrees
 3 - starter motor solenoid +ve
 4 - throttle valve sensor
 5 - ignition coil +ve (supply)
 6 - idle cutout
 7 - TDC sensor
 8 - TDC sensor
 9 - diagnostic
10 - ground
11 - ignition coil -ve

Pin 1 is the first pin from left hand side when looking at the pins on the
digiplext unit.  Pins 1 and 2 normally have no connection to them!

           ---------------------
           Ý  Digiplex Unit    Ý
           Ý                   Ý
         -------------------------
         Ý o o o o o o o o o o o Ý
         -------------------------
           0 0 0 0 0 0 0 0 0 1 1
           1 2 3 4 5 6 7 8 9 0 1