I know this is probably SIAl but forgive me as I'm still a bit of a newbie here really...

AFAIK the previous owner of my car ran it on regular 95 RON unleaded. I'm running the thing purely on Optimax (and have now for some 3k miles). Do I need to reset the ECU in order to fully get the performance of the higher rated fuel? If so how do I go about it? Are there any side effects?

 

It all depends on the age of the car, the older ones yes you need to reset, 97 to 98 will reset them selves but after about a tank of petrol or so 99 to 00 take about 100 miles and the new shape ones do it right away.
....I think im right for the years ?
This site tells you how to do it MRT

.........Ill copy and paste it for you

How to re-set your ECU unit.
ECU clear memory procedure is as follows for auto and manual transmissions:

With engine at operating temperature, turn engine off. Place gear shift lever into park (auto transmission cars only)
Locate the two ECU check connectors, for most cars they are located under the steering column and consist of a black plastic male and female connector, and a green male female connector. The exact location of the connectors varies with the different year models, but generally they are located under the steering column on the drivers side.
NOTE: sometimes they are still taped over with some small amount of plastic tape, so look hard, they will be there!
With the ignition OFF connect black to black and green to green.
Turn on ignition, do not start the engine, (and for auto transmission, cycle the gearshift lever from park to neutral and back to park ), depress the accelerator pedal to full throttle and hold for a few seconds, and then release.
Start engine and then drive for at least one minute, keeping road speed above 11 Km/h.
ECU is now re-set.
At this point the check engine light should start to flash the all clear signal (steady 1/2 second interval flashes). If the check engine light does not flash, or indicates some other sequence, there is a fault present in the system, and should be professionally checked for necessary repairs.
Once, stop the car and turn off the engine.
Disconnect the plugs.
Job complete

Andy

 

93 wrx,the green connects to green,but the black to black wont connect the black with 2 wires coming out has 2 small square conection inside the black sleeve,the other black has a slot so it wont fit on,anybody else had same prob,how do you get a round it !

 

There are three black connectors on my MY99.
Only 2 will connect together.
Keep looking - the third should be there.

 

yea 3 black only two mate ,np, strange, mines a 1994

 

disconnect the battery for a while

 

Read here