History of PO30X Codes

Hi all, hope the new year is off to a great start for everyone. On my 2010 V6 4x4 with ~280,000 miles, I've had a history of PO30X codes over the last 4 years. The first time it happened was in 2019; a PO301 code, CEL, and very rough idle and drive. Smart me did the usual clean the MAF sensor, clean throttle body etc. and also decided to change ALL the coil packs and plugs. Plugs were Bosch and the coil packs were AutoZone super special deluxe whatevers. I know I know ... But no more PO301 and she ran smooth.

That lasted until 2020. Upon return from a little elk expedition in NW CO I got a CEL, rough idle and drive, and a PO303, 05, and 02 codes. I changed the plugs with NGK plugs (all that was available at the time that "fit") and more AutoZone coil packs... cause parts is parts, right??

The next time it happened was in 2023 while up in the mountains on another elk expedition. I hit a big rut and the right front suspension bottomed out/slammed and then it started having a very rough idle/running rough. CEL came on along with disabling traction control. Got down the mountain and to town (Ft Collins ) and the AutoZone scan showed a PO301, 03, 05 and 06 codes. They had no parts available to fix it so I went to the next store - an O'Reilly's. No parts either. Next store down was an Advance. They had parts and tools to loan! I was able to get 6 NGK plugs and 3 regular Advance coil packs and 3 super special Advance coil packs. After a little parking lot mechanic work all was well and we were on our way. Truck ran smooth, CEL off and codes cleared when I checked it at home.

Yesterday while driving to Trader Joe's it started sputtering and running very rough. After a few minutes I got the CEL light with traction control disabled. I scanned the truck and I got the dreaded PO306 code. On the way home I grabbed an ignition coil and plug from Advance and limped home to the garage. Today I swapped #6 coil pack with #4. Took a little ride and the PO306 code moved to #4. I swapped the coil packs back, and put a new one in along with a new Denso plug in #6. I also cleaned the MAF sensor. Runs great, CEL off, and codes cleared. Attached is a pick of the plug i pulled today. It was dry and the gap at 0.46ish. the new plug is next to it for comparison.


I've been going through related threads here to see what I can check beyond doing part swaps. (See below for what I've checked out so far.). Any thoughts/input besides what I have listed? Thank you!

1. Replace all the coil packs and plugs with OEM ones.
2. Compression test cylinders; check for head gasket leaks, coolant in cylinders.
3. Check all the wires/clips going to the coil packs.
4. Clean throttle body.
5. Clean and/or replace fuel injectors.

Threads I've Read So Far:

https://www.tacomaworld.com/threads/cylinder-6-misfire.629562/

https://www.tacomaworld.com/threads/p0306-6-cylinder-misfire.740159/

https://www.tacomaworld.com/threads...30-seconds-that-clears-up-help-needed.276371/

https://www.tacomaworld.com/threads/05-tacoma-p0306-need-your-help.272254/page-2

 

I’d start with 2, 1 and 4. In that order.
And maybe switching back to regular copper plugs.

Monitoring scan data would help too.
Along with freeze frame data of the codes. - You have that handy? If so, post it for us to see.
Maybe some clues in there.

 

Iridiums are fine. I'm on my second set and on original OEM coils. I think it is the coils giving you the problems. You can confirm by swapping out two of the ones with codes, with the remaining two that have no codes, #s 2 & 4. If the code follows, you know it is the coils causing the problem.

Don't the coils you bought have lifetime warranty? The one I got from Autozone once (for another vehicle) had lifetime warranty. The only aftermarket coils I trust are made by Yec Flamma, a Japanese aftermarket manufacturer. I've had good results with them for my wife's former 07 Lexus ES350. I originally got cheapos from Amazon and they barely lasted a year. The Yecs (three of them) were in there five years with no issues when we sold it.

 

Seems to me the shitty parts store coils are you issue (they have all lasted 1-3 years), put OEM (from a known dealer or legit supplier, not Amazon/ebay) ones in and don't look back. Also the stock plugs are copper (Denso K20HR-U11), supposed to be changed every 30k but many people run them well over 100k with no issues.

OEM coils don't fail often but aftermarket ones fail all the time, I don't get why the first thing so many people do when they have a misfire is replace all their good OE coils and/or injectors (that there's probably nothing wrong with) with garbage instead of properly identifying the cause of the misfire the first time and fixing what's actually bad, it's usually much cheaper in the long run than throwing good money away on bad parts. It may be fine to get you out of a jam when nothing else is available but otherwise not a great idea.

 

@TnShooter, I have a rather inexpensive $50 Bluetooth scanner that I use. I will have to see what it has beyond basic code reading/reporting. Thank you!

@Chuy, the code definitely followed where I moved the "bad" coil to. That helped me pin it down this time. My frustration comes in with how often it happens. Kinda like my old Toyota SR5 long bed 4-banger. Every time it rained I would be changing out a bad distributor cap and coil, but the dealer never could ID a reason why. And as for the life time warranty coils, I was spinning my wheels at AutoZone. It wasn't worth the fight.

@Dm93, thanks and agreed. The first time I swapped them out I did the, "they've been on there a 100k...must be time to change 'em" dance. Pretty dumb for sure. On the OE plugs, the service advisor at the dealer said they generally didn't change them until they hit 100k (Temecula Valley Toyota in CA). After this go-around I'm going to do some cleaning and then switch back to all OEM and go from there.