A car that is misfiring might have a vacuum leak. This occurs as air comes in through the intake system and mixes with fuel. If there is too much air coming into the system, the engine's computer may not be able to adjust the fuel flow quickly enough and the car will suddenly and quickly run lean, causing it to sputter. To solve this problem, you'll need to fix the vacuum leak.
Locate the source of the vacuum leak. This can be a bit difficult. You'll need to start the engine and run your hand along all of the hoses on the intake system as well as the hose connected to the brake booster. If there is a large vacuum leak, you will be able to feel it. Visually inspect the hoses for signs of wear, tear or damage. When in doubt, you'll be replacing the hose. You may want to just replace all of the vacuum hoses for good measure if you know there is a vacuum leak but are having trouble locating the exact source of the leak (which is not uncommon).
Loosen the screw on the hose clamp at both ends of the hoses and back the hose clamp off the ends of the hoses.
Pull the hose off the intake piping or the brake booster and replace it. Installation of the hoses is the reverse of removal.
