I have a P0300 code (Random Misfire), it's bad. The Vacuum seems O.K. 17 inches +/- 1/2 inch. The Spark Plugs look fine and the Fuel Filter has been changed. The fuel pump stays steady @ 55 p.S.I with the Ignition off, but fluctuats when the car is running. Is this fluctuation normal when you have a misfire? I have a 2003 Saturn ION.
How much does the fuel pressure gauge move at idle?The most common thing's I have seen cause a miss fire on those is a bad plug coil or module. The plug's get changed every 100,000 mile's on those do have a 100,000 mile's on your car?Have you ever changed the plug's before?You can't always look at the plug and see it's bad. So does the miss fire feel so bad it feel's like at least one of the cylinder's isn't firing at all?