I bought 2002 4Runner V6 3.4L
Well Maintained
Timing Belt / Chain was done maybe 20K ago
Runs Well

Well I get and Engine Light a Few Months Back
Pulled the Code / Random Misfire and Misfire on Cylinder 2
Changed Wires
Switched Spark Plugs
Switched Coil Pack
None of this corrected the problem

Moved on to the Fuel Injectors ( Brand New Denso I belive )

I replaced all of them and still misfire on 2

Head Gasket ? or Possible Air Intake ?

Ill admit there is some cracked piping up top especially just before the throttle body.....

Is that enough to have a focused misfire on Cylinder 2

Funny thing is I don't notice any difference in how it drives

 

It’s possible that you got a defective injector. Unlikely that it would be at the same cylinder, but not impossible.

Have you done a compression test or leak down test to gauge the condition of the cylinders? How about test the coolant for hydrocarbons?

 

I hate to ask what's probably a really stupid question, and I mean absolutely no insult at all, but you DID clear the codes between tests, yes? Once you changed something, like the plug for example, but haven't cleared the code out to ensure it returns.
I'd hate to see something have fixed the problem, but the codes are retained in the ECU's memory, making it SEEM like nothing is working.

I hope this isn't insulting. I don't mean it that way at all...
Pat☺

 

It's a question worth asking. 3.4 codes DO NOT immediately go away when the problem is fixed.

 

Doesn't it use what's called 2-trip logic? It takes two separate, long enough, drives to set, or clear, a particular code?
Doesn't the ECU hold some of the codes it sets in memory no matter what, so that, even if the trouble is fixed, the code, and check engine light, stay, until it's cleared out?
I may be wrong on that, though. I'm not that familiar with the 3.4's.

Good fortune!
Pat☺