Po300-po304 - 2003 Lincoln Navigator

all misfires and bad mixture of fuel and air

https://www.google.com/search?q=05+TAURUS+CODE+SHOWING+po171+po174+po300+pO303+pO304

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PO300 and P1399 are random cylinder misfire detected.
PO301 cylinder 1 misfire
PO302 cylinder 2 misfire
PO304 cylinder 4 misfire
PO306 cylinder 6 misfire
I would say that you have damage to the ignition wiring harness or you ECM is failing.

Code 300 is a random miss not serious enough to peg a cylinder, code 302 is for cylinder 2 and code 304 is cylinder 4. Code 402 is for an EGR flow problem.
Its possible the EGR problem is causing the missfires. The computer sets the 300 codes when RPM drops on a cylinder. The computer does not know why. So it could be spark, fuel, compression, or a vac leak.

THROTTLE POSITION SENSOR, MISFIRE, #4 MISFIRE, KNOCK SENSOR, THESE ARE YOUR TROUBLE CODES, PO120,PO300, PO304, PO325, RESPECTIVELY, REPLACE THE TPS @ THROTTLE BODY, REPLACE KNOCK SENSOR , @ ENGINE BLOCK, REPLACE YOUR SPARK PLUGS & PLUG WIRES ! AND YOU MUST ALSO REPLACE BOTH YOUR AIR & FUEL FILTERS, DISTRIBUTOR CAP & ROTOR , INSPECT, MAY NEED TO REPLACE, I WOULD ANYWAY !!!!!!!! ADD SOME GOOD FUEL INJECTOR CLEANER TO TANK, NEXT FUEL UP !

there is a lot issue with this motor with the po300,po303 ,po304 . it has the do with the head and valves. you need to found out which cylinder is mis firing

The number 2 and number 4 cylinders are misfiring.I would do a tune-up on it sparkplugs, plug wires, air filter and fuel filter.

The p0172 is due to an O2 sensor in the exhaust seeing too much oxygen, the po300 is a missfire present and p0304 is cylinder #4 missfire, check plug and wire to #4 and repair, this should also take care of the p0172, if a cylinder is missing it is just pump air into the exhaust thus causing the code p0172.

The 300 codes are misfire codes, do a tune up and that should fix the problem. the 155 i will have to investigate and try to see what it is.

P)300 ramdom missfire P0304 miss on number four cylinder. try replace number 4 plug

Sounds like you still have air leak.