Are you saying three different cylinders are misfiring? If so, look for something they have in common. Low fuel pressure is one thing. If you have the dual overhead camshafts, check for a jumped timing belt.
Injectors should be replaced in matched sets so they flow the same amount of fuel. If only one or two are replaced, some cylinders will always run a little lean. The oxygen sensors will detect the unburned oxygen in the exhaust and the Engine Computer will command more fuel from all of the injectors.
If there's a leak in the fresh air tube between the mass air flow sensor and the throttle body, some unmeasured air will get in and there won't be any fuel to go with it. That can result in a lean mixture misfire.
The next thing would be to connect a scanner that displays live sensor data so you can see what the Engine Computer is seeing. That will provide some insight as to whether the computer is commanding the wrong amount of fuel based on an incorrect sensor value, or whether the engine is misfiring in spite of correct sensor values. It takes an experienced mechanic to interpret the sensor readings.
Sunday, October 30th, 2011 AT 6:32 PM