have a read of my thread, esp the last page:
HELP! Severe acceleration lag
the switch on the left is mainly used to kill the cruise control when you brake. the switch on the right is for the stop lights so dont worry, your brake lights will still work as they should.
the left switch is also used to tell the ECU when you are braking (don't ask me why Nissan chose to use two switches...) and in a bid to prevent a runaway Toyota situation, the ecu will not let the throttle plates open more than 15 degrees (until you pass 4000rpm) if it detects the brake pedal is pressed. Think of your garden hose when it gets a kink, then you unkink it... wet tshirt due to sudden increase in water flow etc.
I've actually discovered thru a lot of experiments that if your foot is on the brake pedal, the ecu will not let you accelerate faster/open the throttle plates further than its position at the moment you pressed the brake pedal. until you eventually pass approx 4000rpm.
So, if your brake pedal switch is not adjusted correctly or faulty and the ecu is misled to believe your foot is on the brake pedal, grandma's going to leave you at the lights while you're swearing and cursing.
This particular switch on the left is a normally open switch so when you press the pedal, the switch is NOT depressed and therefore circuit is open. The one on the right is normally closed.
So the jumper trick fools the ecu to always think the brake pedal is NOT pressed, by simulating a closed circuit - as if the brake pedal was at rest (which means the switch is depressed).
Eventually, the lag issue will appear again. I think it's because the ecu's failsafe is to assume the driver has to press the brake pedal at least once in X minutes of operation or Y distance has been travelled. I havent triggered it often enough to notice a pattern but both times when the issue reappeared with the jumper in place, it was after driving in heavy stop/start traffic.
hope that helps
see what the dealer says/does and then try my get-you-home trick if they cannot solve it