For the past few years the 4Runner ('98 Limited, 4wd) has occasionally run rough, but no one has ever had a fix that actually prevented it from ever happening again (had plugs/wires replaced, air intake fixed/replaced, and lots of diagnostic visits w/ no result) though the air intake fix did stop it from every running rough and then shutting off while idling, and made the problem disappear for a couple years. So actually, maybe this is not even related.
But what it's doing is that on a road trip home for the Holidays it started running really rough, really vibrating. It also finally produced an error code, P305 I think, it was for a cylinder 5 misfire. We brought it into Toyota in GA and they couldn't find anything wrong.
Then on the way back it kept running rough so we brought it to Toyota in Wilmington and they said the coil and plugs had gone bad and the wires were arcing (coil 5). Mind you, they had replaced the plugs and wires two years ago.
My soon-to-be-ex replaced the coil and plugs. He doesn't know too much about cars, but seemed to do this right. The error code is still there, and it's still running rough. A bit better than before, it's not vibrating quite as much, but I've driven it another 100 mi. since then and nothing traumatic has happened (yet!), it mostly runs rough around 48mph, and a bit smoother w/ the ETC Power on, but is also idling w/ less vibration. But today after a 60 mi. trip (I'm trying to run the gas down to fill it w/ ethane free in case the fuel injector is gunked up) it did smell a bit of burnt rubber after the trip. Any ideas?
I don't know much about the fuel injector theory (we've did injector cleaner on the trip to GA a month ago too), but it did start up not long after we refilled the tank of gas in South Carolina or Georgia, so was wondering if the difference in gas (company/state) could have incited something?

Do you still have an error code or has it been cleared and not come back?

I realize that you replaced the plugs several times, but do you know for a fact that double electrode plugs were used?

As in these:


I am unsure that this would be the cause of your issue - but then it might be.

If you have high miles on the truck, running seafoam through it might help clean up the gunky valves.

It sounds like the standard typical misfire. Cheap plugs, cheap wires - So things that were supposed to last 100k miles don't last 2 years.

Have your future Ex replace the plug wires and plugs. Try to get Denso or NGK parts.

If the problem persits, then the coil pack is going bad and it will need to be replaced.

Thanks! I saw what came out, assuming it was the same as what went in. The plug was more narrow, maybe like what that pic shows inside the coil. Is the plug just the inner part?
It does have 172,000 miles though, so will try the seafoam!!
Thanks for the help!!

I'll find out which brand was used, but he did just replace the coil and plugs. The wires look fine but the dealership diagnostic last week said they were "arcing." With the others replaced, would just the wires be preventing the problem from being solved?

This is a single electrode plug. This is what you do NOT want.


The GROUND electrode is what you want TWO of.

It's rare that plugs cause issues - but it does happen and they're relativley easy to replace if they're the wrong kind.

It is so rare it happened twice for me.


Look at the where it was sparking between the insulator and the base.


Different plug
Cracked insulator almost the whole length of the plug.



Both times, this indicated a cylinder misfire on the check engine light and caused a vibration and loss of power.

I think the Valaro Gas Stations have ethanol free gasoline.

Yesterday it ran pretty well for 45 min. each way drive, but at the end was smelling like burnt rubber and then today it was running rough immediately and making a really strong smell that was like burnt rubber, but maybe also sulphury. Have another appt. to bring it in tomorrow. Fingers crossed that this time it all gets sorted out!!
Thanks again for all the help guys!!

It was the fuel injector! LOL, after the plug, wire and coil had all been replaced and it was still running rough, they figured out it was the fuel injector. Running beautifully now, yay!! Good to have it back to norm!!

Unfortunately mine is doing the same thing. How much did they charge to replace the injector?
Thanks

It's around $250 for a new set of injectors. Denso Fuel Injector Upgrade Set for 3.4L V6 4Runner Tacoma and Tundra – HP831 – MotorWest Performance They're pretty easy to get to in my opinion. Just take off the intake manifolds and loosen the upper timing belt covers.

My mechanic insisted it was everything but the injectors, he was wrong. If you replace the plugs and wires, it can't really be anything else especially when the code keeps coming up.

The injectors should be around between 13.4 ohms to 17 ohms. Just replace the injector that's bad with a oem. I had bad luck with refurbished injector or get em refurbished.
There is a old school guy here that really does a great job.
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Could also be a valvetrain/compression issue. Could also be a failing coil pack. I had a bad coil pack that only caused a misfire on 1 cylinder and not both cylinders it serviced.