misfire problem

2000 tacoma 3.4L 406000kms

Truck has misfired again, after a few months of running good.

In the past around 399000kms the truck had issues misfiring, Changed all ignition components, plugs, wire, and coils, truck continued to run decent after this, only sometimes getting slightly shaky on the highway, but overall good, took it on road trips and it was fine etc. Once or twice early on it shook a spark plug wire loose from the plug and I just pulled over and pushed them all firm back in. have had 12.3L per 100km on a mixture of highway and city driving, pretty decent. I had chalked the shaking up to something entirely different like stabilizer bushing.

yesterday I had a misfire, got a code for cylinder 4, last time it was cylinder 6. I have read that the fuel injectors can go bad around this age, but not sure if my symptoms align with fuel injectors or possibly intake manifold gaskets. Doubt that the ignition components would be problematic after only 6-7 thousand kms, IDK if pulling the spark plugs would give me any indication. Valve cover gasket was replaced recently, cant really think that this would be compression issue but maybe timing related? other than that feel like im left with fuel injection issue or an air leak.

Anyone know a good method to test my injectors without being too invasive? or anything I can do to look into this further?

 

I gave it another look, was able to get a screwdriver stethoscope onto 5 out of 6 fuel injectors and hear them ticking as the engine ran, all sounded good not missing a beat, was not able to test cylinder 5 fuel injector it was too hard to reach. Double checked all air hoses and air filter and everything looks good aside from stale hoses that I have been meaning to replace for a while but shouldn't be causing anything major.

 

I have pulled spark plugs for cylinder 4 and 5 pictures attached, don't know if this is normal or extra fouled. https://imgur.com/a/Q3S8xZd