[hobosapien]

140k miles

You got that right - it's throwing codes on all 8 of them. Thing is, I do not feel a rough idle regularly, and I do not hear or feel it when driving. It drives fine! I took it to the dealership for a diagnostic and they told me the coils need to be replaced for $1k which is ridiculous. Had another mechanic look at it and he didn't necessarily suggest replacing the coils. What are the odds that it's happening to all 8 of them? My understanding is that you only replace the ones that have issues, and even then it's rare to encounter since they are indestructible.

Perhaps an ECU/computer issue? Would it need to be reflashed?

[TowMeOut]

Silly question...when's the last time the plugs were replaced?? Any chance they're either worn out or oil fouled??

Yeah, all 8 coil packs going bad at the same time sounds pretty sketchy. Could it be more of a crank position sensor issue that's manifesting as misfire?

[hobosapien]

Originally Posted by TowMeOut

Silly question...when's the last time the plugs were replaced?? Any chance they're either worn out or oil fouled??

Yeah, all 8 coil packs going bad at the same time sounds pretty sketchy. Could it be more of a crank position sensor issue that's manifesting as misfire?

They were replaced about 35-40k miles ago, so I would hope they don't need to be again.

If I may ask, what do you mean by crank position sensor?

[TowMeOut]

Just kind of thinking out loud. Since the 4.7L has no distributor (hence the coil packs), the computer needs to know where the crankshaft is in the combustion cycle. So....it uses a crank position sensor and some other sensors to figure out when to fire the spark plugs...... If that's out of sync wouldn't that make all the plugs misfire? I'd think the "mechanic" at the dealership or elsewhere would do some more diagnostics before just telling you to replace all the coils....

I'm guessing you're getting P0300 codes....there's a laundry list of other stuff to check before you start replacing coils, at least according to the FSM.

http://4runnerclub.com/i/4r_files/fs...rr/0060011.pdf

http://4runnerclub.com/i/4r_files/fs...r/00600610.pdf

http://4runnerclub.com/i/4r_files/fs...r/00600410.pdf

[bpchura]

Coils do fail but not that often and to have all go out at once is borderline impossible. Some cars have all the coils built into one but I believe 4runners have coil on plug so they're all separate. Id also guess it would be a sensor issue or maybe a loose connection somewhere? Interesting that you're not feeling anything. If it were misfiring that bad, you'd for sure know.

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[TowMeOut]

Check engine light with all cylinders misfiring and vsc trac lights on

Another thread but similar description. Maybe the fuel pump is on the way out (low fuel pressure) or a clogged filter. OP claims he throws in some fuel injector cleaner and all is well. That sounds sketchy but I suppose starving of fuel (or at least the computer thinking so) would throw misfire codes.

[bdogfromtexas]

Did you ever figure out a solution to this issue? I drive a 2004 4.7L V8 and am about to replace the spark plugs but looking at other possible solutions if that does not fix it.

[Inv4drZm]

Originally Posted by bdogfromtexas

Did you ever figure out a solution to this issue? I drive a 2004 4.7L V8 and am about to replace the spark plugs but looking at other possible solutions if that does not fix it.

Check the battery first.

[bdogfromtexas]

Originally Posted by Inv4drZm

Check the battery first.

I'm at 198k and we bought this one at 172k and cannot find any history of spark plugs being replaced. Somewhat rough idle at times, Cylinder misfire 1-8. The battery was replaced in November so I doubt it's that.

[03v84Running]

Think plugs would be a good place to start, here are some other possibilities

Toyota P0300 Causes
(* = Most Common)

Faulty or worn spark plugs *
Faulty spark plug wires or coils *
Distributor failure *
Faulty fuel injector *
Vacuum leak
Low fuel pressure
Camshaft sensor defective
Crankshaft sensor defective
Engine timing off
Leaking head gasket
Low engine compression
Poor quality fuel

[4RunnerAquasport]

Any outside chance of rodent damage? A partially chewed wire could result in low voltage signals being distorted getting back to the ECU. It's a long shot for the rodent thing, but all 8 coils going bad at the same time? Dealers...SMH.

[hobosapien]

No idea what the issue was but I noticed that if I ran the A/C the engine lights would trigger. However if I turned the A/C off and drove 80+ mile (the amount of distance it takes to cycle the ECU) it would go away. So for some strange reason the A/C was triggering the lights. As much as I tried to have it investigated no shop could definitively tell me what was wrong.