On early MYs (especially pre MY97) the ECU retards the ignition when knock is detected, however, it is very slow to advance the timing again. An ECU reset will restore the car to factory default settings. This will remove any stored fault codes and restore ignition advance. It is possible to reset the ECU by following these steps:

1. Turn ignition OFF
2. Connect Read Memory Connectors & Test Mode Connectors (jumper 5) [black connectors] – (jumper 6) [green connectors]
3. Turn ignition ON (engine off)
4. Engine Check lamp turns on
5. Depress accelerator pedal completely
6. Then return it to the half-throttle position and hold it there for two seconds
7. Release pedal completely
8. Start engine
9. Code is indicated by Pulsing lamp
10. If a fault is detected – Check ECU Code
11. If no fault is detected – drive the car sensible for a couple of minutes i.e. until warm (do not run tall & do not thrash it!)
12. When the ECU has been reset the Check Engine Light will flash
13. Code is indicated by Pulsing lamp
14. If a fault is detected Check ECU Code
15. Turn ignition OFF & Disconnect Connectors
16. If there is a fault Check Appropriate Sensor