2004 Corolla with 255,000 miles on it. I'm getting the code for cylinder 2 misfire, a P0302. The CEL came on last week and I thought the easiest answer was to change the spark plugs, so I changed them all. Well, yesterday the CEL came on and I got the same code. The next thing I can think of is a coil has gone bad. I guess I could switch the #2 with the #3, and see if a code for Cyl. 3 misfire. There aren't any other codes popping up. Last year I got the code for too lean, which was the P10170 (I think), so I changed the intake gasket, and the fact that I'm only getting the P0302 leads me to just focus on that one cylinder.

Thoughts?

Ignition coil would be the first thing I check.  Take a look at the plug boots and make sure they aren't cracked or worn.  Same with plug wires.

Rough idle after replacing and it could be crank/cam position sensor?


ETA: I chased the same problem recently on a jeep I6.

I only notice it stumbling right at start up. If I let it run for a minute, it runs fine. I can pull the boot while its running and it will stumble. The code always comes on after cranking it up. I need to check and see if there is any oil on the boot too. I didn't notice it last time. Could be a bad valve cover gasket too.

Well, that wouldn't be a bad idea.

I replaced my coil and the cel cleared for 30 minutes.  Pulled my boots and wires...No problem there.

I'd just put in New plugs 15k miles ago so I figured they were fine.

Had a buddy run a compression test, came back at 130 per cylinder so I knew that was good (valves, rings, gaskets).

Come to find out, plug #1 was borked.  Tiny crack that caused some arcing.  Now running fine.


I bring up the cam and crank sensors b/c they created a similar issue as above for me.  Took an entire day just to track that one down.

Good luck man.  I hate electrical problems.

If it only runs like crap on initial start up after a long soak, you may have an injector leaking and flooding/fouling the plug on that cylinder. After it starts, it clears out the excess fuel and all is fine until the next morning.
PS: Toyota injectors are very reliable but anything is possible with a car.

Well, I switch coils #1 and #2, thinking if it was a bad coil then I would get a Cyl #1 misfire now. I didn't. After resetting the CEL, I'm still getting a #2 misfire. I checked the injectors by manually pulling the electrical connections to see if the idle stumbled, and it did on all 4 cylinders. Then I check the ohms of the injectors, and they were all the same. So I can't figure out what is causing the misfire. I guess I'll check the compression and see if I have bad valves or something.

Any ideas?

With that many miles, the injector on #2 may be firing, but the spray pattern could be bad/partial if it's failing. If it's cheap, I'd pick up a new injector, and/or swap injectors from another cylinder and see if the misfire moves.

I'll give that a shot

Any luck?

Bad head gasket

sorry to hear that man.