Not sure if you have resolved this but I think it is worth mentioning that the Mk 1 1.6 was generally designed to run rich. The ECU is not reprogrammeable but I have heard mention of the use of a crystal to make the standard ECU richen the mixture even more. This in turn increases the power output and rev range. Clearly this is a rough an ready approach to improving performance.
As the ecu is not programable then I would question the use of a rolling road tune up as these I believe are more designed to get programmable ecu's to give the best settings for power economy etc. I would suggest that you look at Aldron race tuning they are on the internet and are based in Brierly Hill Dudley. If you wanted to go he performance route I am sure they could supply and fit a programmable ecu and tune your car.
However if all you want is to get the car running smoothly then as the first post suggested a good service may be all you need replacing filters ect can make a big diference. On removing the plugs check the condition ( See any haynes manual for what to look for) if black dry then you are running rich if oily then oil is getting into the combustion chamber again making the mixture richer. Also check the specification of the plug as they are designed to run at different tempuratures. The other thing to check is the cam angle and any reputable garage should be able to check this. Stock its 10 degrees BTDC if it less then this can lead to incomplete combustion and loss of performance. If you do have it checked and adjusted you may want to consier advancing it to 14 degrees BTDC as this leads to a useful power gain but be aware that you will need to assess this for your engine as there is an increased risk of pinking.
The second post mentions the fault code check. This will tell you if any of the sensors are at fault and need changing.
Hope this helps Ron