OK from OAP ....12v can be given any way round and wont affect operation...3 mins to fully close not bad...but remember the voltage is higher once on the engine running as the voltage to the valve only there with engine running...ie...13.8 volt...also it recieves heat from the engine bay which it needs...as this slows down the opening , so stopping to get fuel or any short stops [ engine off ]...you return to car start and only small increase [ if any ] of RPM....to add this unit should not be adjusted...there pre set back in the day......the small 7mm nut at rear was sealed with yellow wax...if ever the wax is broken...you will know someone has been playing !!...this will upset the operation, saw this many times back in the day by people who did not understand the system...so if your ones show no sign of yellow sealent cracked....ide say you have 4 perfect ones, Peter