When you let go of the gas pedal the dashpot keeps the throttle open for a second or 2 to help burn off any excess fuel. Its an emissions device. My 89 5spd 22re had one but the adjusting screw had been removed. When i put an adjusting screw in and set it to spec (2000rpm for mine), i quickly realized why the previous owner had removed the screw, the dashpot was stuck and wouldnt allow the idle to come down back to normal. This caused high idling and when i would press the brakes the rpms would go up and down. So i bought a new one from the dealership (about $50) and installed it. I noticed an improvement in driveability when shifting gears. With the throttle staying open for a lil longer it helped make the gear shifts smoother. Just my experience.