Hey guys so I wouldn't post on here if I didn't do my research first! Searched up and down my Owner's Manual, Repair Manual, and Acurazine to find solutions. I see that this is ONLY a problem with the 2004 Acura TL 6MT. I am getting PO300-PO306 Random Misfires in ALL cylinders. I ruled out a mechanical issue as it comes and goes. It starts to misfire then it goes away so I reset CEL and it comes back after driving maybe 10 miles. I am the second owner and have driven it 20k miles since owning so we can rule out previous owner destroying it. ALL Maintenance is done on the vehicle at 120k miles. Timing belt+tensioners at 105k, Water pump at 105k, Spark plugs at 105k, Compliance bushing etc etc. Valve Adjustment was done a little later at 115k. ALL VALVES ARE IN SPEC. It is my race car as I own another 2006 Acura TL 5AT. I do get on this thing but not as much as I've seen others do. I pump 93 Shell+V-Power RELIGIOUSLY. Previous owner did as well. Never money shifted so don't tell me its a bent or burnt valve. Car started misfiring in a random parking lot as I through it in neutral to wait in a drive through line. Car started shaking and CEL was flashing so I knew it was a misfire. Let the car sit overnight and drove the daily. Started it up the next morning and the car was FINE. I suspected it was the Spark plugs so for shits and giggles I changed those out and when I pulled them out they looked MINT. So new spark plugs. I went for testing each cylinder's coils and they all seem to be working (WILL BE REPLACING ALL). People are suggesting it could be a clogged Cat? I have the RV6 V3 High Flow Precats. The cat seems to be working fine as the Cat is hotter in the rear than in the front so it's doing it job but I will rip that out and check to see if it melted or shattered. Nobody has found a definite solution to this and I was wondering if anybody could chime in. People are going to tell me ECU Reflash but I read on here that is only a problem when the car is revved over 4k RPMS. This misfire is occurring at idle and disappears after 3k RPMS. So far the plugs were changed and I filled up at a different gas station and dumped fuel injection cleaner to see if that helps and so far it DID. I pumped the gas and put the injector cleaner in it and at that first light the misfires stopped. For shits and giggles I tested the timing and put it under VTEC WOT. Car took the power amazingly as it usually does but I'm afraid the misfires are going to return. Has anybody had any luck by changing the Plug wires? I am going to clean out the EGR today and maybe change coils. My buddy is a Honda tech (used to work at Acura but we all know how Acura dealerships are) so he is going to sneak it in today and run it on the diagnostic machine to see what is actively happening to my car.

bent valves. either previous owner or you performed the money shift.
I came to this conclusion because of this statement "at idle, it misfires...but goes away at speed" Classic case of damaging valves.

FYI; my friend fucked my heads up by doing exactly this. downshifted from 4 to 2 at 90mph. Pistons kissed heads and the rest is HISTORY.

to confirm, have a leak down and compression test done, THIS WILL TELL YOU EXACTLY IF YOU FUCKED YOUR HEADS

NEVER HAVE I EVER MONEY SHIFTED EVER. No way previous owner did because it would have surface shortly after purchasing vehicle. Not 20k miles later.

^not true.

Have your friend at honda apply the update and also get a compression and leak down test to confirm. The test will confirm. it's pointless to guess.

I do a lot of track time with this car and previously owned a 93 300zx Twin Turbskies and never money shifted a day in my life. (knock on wood)

Roger Dodger! I will suggest the Compression and Leak Down tests. If they come back inconclusive OR they show low compression?

one step at a time. Get the test performed. then go from there

FYI; mine was misfiring in ALL cylinders too. (what the CEL said) but it would be random. and at idle it was super angry...but when driving it was fine.... CLASSIC case of Piston hitting valves

Did you money shift?

my friend was driving my car.
I just looked at pictures....May 31-June1 2014 was the night it happened.

Well my point exactly. Is there ANY OTHER WAY the Valve can come in contact with the Piston without money shifting OR bad timing?

what is your point? lol

GET THE TEST DONE. and find out for sure

Well my point was I'm almost positive its not a bent valve because that is what Uriel suggested as well. But I never money shifting and neither did previous owner. My timing is good too and that was done 15k miles ago at Acura. But yeah I guess I'm gonna leave it up to my friend and he should be able to pin point the problem. Thanks for the input.

report back with test results.

Valve float.

https://mechanics.stackexchange.com/...impact-engines

water can do it too.

Valve Float is caused by money shifting

troubleshoot the coils. have the engine running and disconnect the coil harness one by one. if engine note changes, BAD coilpack

No money shift here, holmes:

https://acurazine.com/forums/second-...y-case-446281/

Post #9 has the best assessment.

OOo personal expericen!

I would think this if only the car didn't return to normal and I did a WOT on 4th going 130mph. I would have experienced major loss of power if it was a bent valve. Car was dyno'd at 284 at the wheels 5k miles ago so not really experiencing and sort of loss from the power

The only reason why I say that is if it skipped timing I wouldn't have all my ponies

It does appear, from your original post, that you have done your homework thoroughly; however, you do admit that 'it is my race car...' and further acknowledge 'to getting on it' in a self-measured way compared to 'others'; so, my point is 'stuff' happens even though you may consider your driving style non-aggressive.

Like justn stated have the testing done, keep an open mind; hopefully, it's just a bunch of f'ed coilpacks and you're golden.

Thanks man! I normally don't resort to forum posting for this kind of stuff. Don't consider myself a certified mechanic but I definitely know my shit. Yeah I'll get the tests done as well as looking into my ceramic coated HFPCs to see if they're fucked up and causing it

trouble shoot the coil packs. but based on your description, it's EXACTLY like mine

- random misfires
- only at idle
- smooth ride at speed

I did troubleshoot em and they all seemed in good working order.
Apparently this type of intermittent misfire can be caused by a number of things.
CPS sensor on it's way out
Clogged fuel rail
Failing fuel pump
Plug on it's way out
Coil on it's way out
Wiring on it's way out
Cats getting clogged.
Bent valves
Burnt valves
Tight exhaust valves.

So many causes for this! Even the ECU itself could be hurting it's own motor 😭

I'm making light of the situation and I'm calling it. "Subaru Mode" since the bitch sounds like a Box 4Cyl lol

lol that DEF. is smacked valves.

you are def. running on only 3 or 4 cylinders

my car and my friends 05 6MT TL sounded like that, and we both joked that it sounded like a boxer engine

Then why is it going back to normal on it's 280hp?

iunno, whatchu talkin bout...my fully bolted 6MT is only pushing 241 to the wheels, and it's running correctly.
unless you have Bisi Stage 3 cams (no wonder why it's making that sound) you cant possibly be at 280

Don't talk about my awesome power now! But why would it just come back if the valves were bent?

Port and Polished Intake Runners TB Manifold. Stayed with Aluminum vice magnesium for better compression. P2R Runner Spacer etc etc don't want to go into mods atm

i have all that shit. and i have pre-cat deletes.
i am fully bolted on bro. There is NO WAY you're TOUCHING 280

When I get home I'll sift through my parts box and find the dyno sheet. You tuned?

unless you're cammed, which would explain the idle noise....and the 280hp.

i'm planning to drop the $1700 on Type-S 6MT ECU + Hondata next month.

Run a piggyback or get a cheaper 07 Base AT ECU. It's tunable. Just hate matching wire harnesses

no, I want the Type-s 6MT ECU + Hondata + nav harness. it's $1700.
All plug and play for me

also, I keep lol'ing at boxer engine sound. that DEF. convinces me you're only running on 3 or 4 cylinders.

also, running on 4 cylinders, I still beat a 4cylinder accord

please crab man, didn't we just goes through this one?