Originally Posted by n0v8or

While the word "misfire" naturally inspires a mental image of a missing spark; however, that is not how the term is defined by automotive engineers. Their definition is more broad in scope.
The engine control computer ("ECU") monitors the angular velocity of the flywheel. As an example, a spinning Ferris wheel rider does not make any net forward progress, but they are moving nonetheless. If the seats are located 30 feet from the center of the apparatus, the rider travels approximately 189 feet during every rotation. If one rotation requires 30 seconds, the rider's velocity is approximately 378 feet per minute.
The ECU samples the angular velocity of the flywheel immediately before and after each piston power stroke. If the instantaneous angular velocity at the end of the power stroke is not higher than it was at the beginning of the stroke, then no energy was transferred to the crankshaft during that stroke, which is defined as a "misfire". The ECU "knows" which cylinder (or cylinders) is responsible for every misfire, and how many have occurred consecutively.

While a missing spark is a common cause of a misfire, it is not the only cause. Air, fuel, spark, compression, properly positioned valves, and correct timing are all necessary for combustion to occur. If any of these are not present or inadequate, a misfire can result. Other common misfire causes are fuel injectors, stale or contaminated gasoline, low compression, incorrect air/fuel ratio, variable valve timing control error, worn valve train components, and "stuck" valves.

Toyota spark coils have internal electronic circuits that verify a spark actually occurred and feed that information back to the ECU. Position of the variable valve timing mechanism is monitored by camshaft position sensors and is also sent to the ECU. If either the ignition or variable valve systems were the cause of the misfire, likely an additional fault code would have been set in addition to P030x. The fuel injectors, however, are not monitored.

Originally Posted by Roscol

Swap the plugs and see what happens, you’ve ruled out coils, now we need to prove if it’s just a bad plug.

Originally Posted by ACP84

I swapped the plugs yesterday but the spark plug on cylinder 3 seems fine but who knows at this point. If the code comes back on cylinder 4 then It looks like it was the spark plug. If it still happens on Cylinder 3 what are my options?

Originally Posted by n0v8or

Or possibly electrodes were damaged during shipment or installation. Iridium electrodes are more fragile than platinum or copper. In this case, Roscol still wins .

A mechanic would probaly perform tests in order of least required effort.
-1- Check fuel trim scan data to see if ECU is adding fuel, perhaps to compensate for restricted injector nozzles.
-2- Cylinder compression check.

Originally Posted by MxdMenace

Hello,

I recently experienced the same issues on my 80k km 17 NX200T Fsport. P302 code for cyl 2 misfire. Changed to new plugs and swapped coils and same P302 came back. At one point car went into limp mode.

Dealer discovered another code for all cyl misfire. Turns out there was a TSB for defective cylinder heads on early models and my symptoms matched the TSB. New head replaced under warranty (new Toyota part number so something has been updated). Something about the valve guides being misaligned causing the valves to not seat and lose compression causing the misfire.

no issues after replacement.