Purge valve would be fitted to the charcoal cannister on the RHS inner wing behind the header tank. All the emisioins (breathing) from the fuel tank passes through this to collect any hydrocarbon emisions. When the engine is running above idle but not flat out the purge val;ve opens and the engine draws air back through the cannister to lift the hydrocarbons from the carbon screen and burn them in the engine. Think backflush.
Anyway, you can safely leave it alone, if you fit a TSR for no lambdas the ECU will ignore it.
