P0304 - 2005 Dodge Neon

I would say you have more that one code fault and they just used a cheap scan tool. You need an auto electrician with a pro grade scan tool computer. That is the only thing that can diagnose the engine speed sensor.

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What the P0304 code means. The P0304 code will be seen in cars where the ECU has detected that cylinder 4 is not firing properly. The ECU monitors the operation of all cylinders to ensure they are all firing on time, so when one misfires repeatedly, a Check Engine Light is set.

P0304 OBD-II Trouble Code: Cylinder 4 Misfire Detected

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Question edited. It is 'P-Zero', not 'P-Letter Oh'.

Help in the link. By substitution and swapping the parts you have, you can work out what part is faulty, or just take it to an auto-electrician.

https://www.google.com/search?q=2001+Kia+Rio+P0304

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Misfire could be coil issue or poor compression depending at what point it misfires.
EVAP issue could be a leaking fuel filler cap or an air leak in the vacuum pipes.

P0300: Random Cylinder Misfire Condition
http://www.autocodes.com/p0300_toyota.html

P0301: Cylinder 1 Misfire Detected
http://www.autocodes.com/p0301_toyota.html

P0304: Cylinder 4 Misfire Detected
http://www.autocodes.com/p0304_volkswagen.html

The P0304 code means that the cylinder 4 is misfiring or is ... P0304 MAZDA P0304 ... Engine Light ON? The Engine-Codes.com ELM327 WiFi Car Diagnostic
OBD II Trouble Code Information and Diagnosis Engine Codes com Welcome to Engine Codes

My F150 2006 5.4 shakes and rattles at certain speeds the code comes up as P0304 have recently changed plugs

A P0304 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #4.

A code P0304 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

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I have an 2002 Kia sedona the code p0304 means an 4 cylinder misfire and also the wiring and plugs.I noticed an while back that when I press the gas smoke will come from my tailpipe and now my van is hesitating to go and it stumbles and the check engine light is on,I have the same code p0304.

P0304 means that you have a misfire on cylinder #4.Pending code are secondary indicators to let the mechanic know that the problem is more or less constant even if it is a random missfire.

P0304 is Misfire in cyl# 4. Check your ignition system and fuel system.

P0421 is Catilist effeciency. Fix P0304, if P0421 returns you will need a catalitic converter

P0455 is an Evaportive emission leak. Be sure you gas cap is tight and secure. If it is ok, then there is a leak in the system.