a worn valve will make it back fire
There are a couple of reasons why a 1999 Ford Contour may misfire. The spark plugs may need changed or the coil pack may be bad.
Spark plugs
It means # 3 cylinder has a misfire. My advice is to replace all the spark plugs, and check the spark plug wires carefully.
P0300 : multilple misifreP0302 : misfire cylinder #2Check plugs, wires, injector, compression, etc.see related question below.P0300 : multilple misifreP0302 : misfire cylinder #2Check plugs, wires, injector, compression, etc.see related question below.
If the parts you mentioned have been tested and proven good, possibly the wires were not connected to the right plugs if recently changed, or out of timing.
p0302 is cylinder 2 misfire, you need to fix the cause of the misfire. Possible causes are plugs, coils, injectors......
P0303 is cylinder #3 misfire. P0300 would be random misfire. Either way you need to diagnose the case of a misfire. Check spark plugs, plug wires(if equipped), cylinder compression, fuel inectors, and wiring.
P0302 is a cylinder number two misfire. Causes include spark plugs, injector, internal engine failure, etc.
I have a 95, had a misfire... mine was because of the plug wires... changed the wires and plugs mis fire stopped...
Change spark plugs and wires... TUNE-UP...
Plugs or / and Coil Packs. Auto Zone will check your codes for free and will tell you which plugs or coils are bad. Then replace.
Trouble code P0300 means: Multiple Cylinder Misfire Trouble code P0302 means: Cylinder 2 Misfire Detected Trouble code P0303 means: Cylinder 3 Misfire Detected I would change plugs and wires