Intermittent Misfire Issue

Hello, 2008 2.7L 4x4 5speed 168k miles Tacoma, recently purchased. Having a very odd intermittent misfire issue, got my mind boggled.

Every few days or so I will misfire ONLY on cold startup (usually in the morning). It is extremely short (half a second) and goes away and runs smooth. The idle is low and it vibrates extensively for that split second. Throws a code, always P0303 cyl 3 misfire (never another cylinder). I delete the code with my code reader and restart the truck and it runs perfect. The first time it happen i moved the coil from cyl 3 to 4, and replaced all the plugs with oem denso. The issue never followed, always cyl 3.

Recently I have noticed it will get slightly slower (minorly down on power) leading up to the next code throwing misfire session, and will "catch" itself on startup (hang at 1000 rpms for a minute or so before the normal high 1500ish cold idle before usual dwindle down as warms up) the time before the misfire startup session, so I can usually tell when it will happen next. Once it happens again, I do nothing but delete the code and we are back to full power (again not too much of a difference but definitely noticeable).

Looked into the ecu history with my codereader and there are only 7 registered misfires on cylinder 3, so very minor, and the CEL never flashes when it appears, always solid so I believe that means the misfire is not current.

I have tested all electrical connectors relating to cylinder 3, such as the injector and coil wiring by pulling and wiggling all wires while the truck is running, thinking it may be a loose connector, nope. MAF live output is within spec, about 0.01 lb/s at idle and 0.025 lb/s at 2500rpm, O2 sensor output is good, injectors all seem to be firing good, did the old teeth to screwdriver to injector to feel the clicks while running.

I plan on cleaning the throttle body, as the idle is low after disconnecting and reconnecting the battery while the ecu relearns the idle, but I think that is unrelated to the intermittent misfire problem.

Any ideas? going crazy over here. Would love to not break out the ole compression and leak down tester.

Thank you.

 

Try swapping that coil to another cylinder as a way to rule out the coil.

 

Very common symptom of a slowly leaking headgasket.

The coolant mists overnight into the cylinder and causes a very brief misfire on cold start.

It's hard to confirm, a borescope after getting it hot and pressurized then watching the cylinder in question is how I start.

 

I already did that, did not follow.

 

Okay thankyou. Would I be experiencing any other head gasket symptoms? I have no loss of coolant, no coolant in oil, and no smoke at all.

 

No one ever reports the loss of coolant its hard to detect as it is so small.

Cold start misfire is the only symptom to start with.

 

Alright, I will try to boroscope, but I may be do the exhaust gas test on the overflow tank (color thing) and also a leak down. Out of curiosity, in your opinion is it easier to do a head gasket, or to just try and find another 2rz-fe to swap in? I see reman blocks for around 3k online, not sure if they are any good. Of course only if the head gasket is bad.

 

100% headgasket repair. We see used engines with the same symptoms.

I've never had success with the gas tester/chemical test on any toyota headgasket for some reason.

What I usually see is the tiny combustion bubbles in the coolant through a funnel once warm and reving. But they never cause the chemical to change to blue for some reason.

 

For what it’s worth, spark plug tube gaskets (and new coils) seem to have fixed my problem.

 

Okay, is it possible to see the bubbles through the reservoir? haven't noticed any yet. I guess the best test would be leak down for confirmation on head gasket. Still holding out hope that is not the case though, and I have just a leaky injector or something.

 

Did not notice any oil on my plugs or coils when I replaced the plugs. Would that indicate non-leaking tube gaskets? Thanks.

 

It only shows in the top of the rad fill or a fill funnel.

Leak down typically doesnt show because the leak happens on cool down slowly, but its worth a shot.

 

Maybe try new coils since you’ll be going down that road eventually. Sorry but I’m a parts cannon, guy.

 

Appreciate it, thank you. Pretty much eliminated the coils as the code did not follow coil on previous occurrences, not currently in a parts cannon position lol.

 

Alright, will boroscope when hot, and take my rad cap off and let it warm up to observe for bubbles. Realistically how bad is this lol, head gasket problem so miniscule it doesn't show up on leak down has me thinking to leave it for the time being.

 

It gets annoying, where I am we remote start so we'd never even see it if it wasnt for the check engine light.

I may be wrong, but just sharing my experiences. Best wishes.

 

Thank you, out of curiosity do you know if the 2.7 has a cold start injector?

 

Just as an update:

Did compression test and cleaned throttle body today. Throttle body cleaning made it idle much nicer on startup, not thinking thats the solution, but will note it.

Performed compression test with hot engine and all plugs out. I did nothing for the efi however, just unplugged the coils and took out the plugs, because quite frankly I forgot. Got 145psi on every cylinder, almost exactly the same across the board...literally. So I am happy with that, but assuming if the head gasket is leaking, its small enough to not show up on compression test. Once again these cylinders were essentially identical.

Boroscoped the cylinders, 3 looked a bit "glisteny" but so did the others to an extent, was really hard to tell. Again this was a hot check, right after I got home from work.

I guess my next step is to do a leak down test, if that comes back inconclusive I will just leave the tester on overnight and see if it drops during that time by the next day.

Just to note, after the compression test I had an immediate CEL P2433 for secondary air injection, not sure whats up there, I unplugged and plugged back in as well as deleted the code and it has not come back.

Let me know any other suggestions, I will continue to post updates, if for no other reason then to help future troubleshooters with a similar problem.

Thanks.