What causes a random cylinder misfire code?

Could be the need fot new plug wires and a tuneup.

Could be moisture settling in the sparkplug boots in the plug valleys that cause arching during cold starts until it heats up and evaporates, which would still be cause for replacement of the wires and plugs. Possible that you could have some water or other contaminents in the fuel system that is circulating around. if it does it in top gear when giving it throttle, then I would be let to believe that its probably ignition related. When uder a load which is at cold start up and during certain times you have stated, marginal plug wires that are arching will arch more often. If you pull the wires off the coil packs and plugs to inspect, you might see some carbon spots where they have been arching. When the car is running ok, you can also take a spray bottle with just water in it eand spray around on the plug wires at both enda ans sometimes get it to start missing if it is indeed that problem, or doing it at night will reveal visible arching that might be occuring. If its not doing it often, it just may be somthing that you need to wait for it to get worse so that you arent chasing an elusive ghost. Until it gets BAD, its not really hurting anything other than flagging a code and causing you a small loss of gas milage and irritation.

Random Cylinder Misfire

Random Misfire

That the symptoms happen when cold points to a fuel problem. Ignition problems are usually worse when hot. I would start with cleaning the throttle body and adding fuel injector cleaner to the tank if you have not been using top tier gasoline brands regularly. However, if the ignition tune-up is due get that taken care of because a weak ignition can worsen the behavior of a fuel mixture problem.

P0300, random/multiple misfire, is a slippery code. It does not come from a sensor but is computed within the ECU based on the time it takes for the crank to transition between cylinders. The ECU knows how long it will take based on the engine speed and if a cylinder makes a habit of taking longer to get to the next one it is deemed to be misfiring. This leads to a lot of false reports but based on your description it is actually happening in your engine.

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What causes a random cylinder misfire code?

My 2002 Nissan Spec V has had intermittent random cylinder misfires for the last 20k miles or so. I realize this is bad, however, when taking the car in, it has never been able to be reproduced in the shop, so they say they can't diagnose the problem. The misfiring typically happens when the...

The random missfire is most likely caused by your lean running condition. Possible causes of leaning out are a vacuum leak, not enough fuel pressure or volume from a weak pump or plugged sock, faulty sensor like the mass air flow or manifold absolute pressure sensors, faulty injectors, faulty computer, faulty ignition control module, loose electrical connection, or wire damage somewhere. Most likely it's a big vacuum leak, but fuel pumps and MAF sensors are notorious for failing in GMs of this vintage. To check your MAF, SOMEtimes you can cause a failure or improvement on how it runs by lightly tapping on it and listening to the engine for changes or fluctuating in RPM. There shouldn't be any change if the sensor is good. Another simple check is to disconnect the sensor (forcing the computer to run at a predetermined level of air flow), and running or driving the car. If it seems to improve, chances are the sensor is faulty. Take note this will trigger a trouble code for the MAF. If your wondering where it is, it's in the air inlet located between the air filter box and rubber boot running to the throttle body. To check for a vacuum leak, simply start the engine, open the hood, and carefully listen around for a gushing kind of sucking noise. These are just some things to check, I hope this helps and good luck to you.

May just need a regular tune up, plugs, fuel filter etc.also intake plenum cleaned and plug wires. Your problem should have turned check engine light on. Also get an OBD2 scan that should tell them what's causing problem if they have a good tech.Hopefully you didn't mess up cat. converter by waiting so long. Good luck.

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check for vacuum leaks especially around intake and throttle body and check ignition voltage output good luck

Disconnect the battery for 10 minutes to clear the codes after you change the fuel filter.

Coil.