[JWaldz]

Alright, so I'm making this thread as a go by for others when researching the code. I know there's a few already out there, but most are dead ends with no resolution. Hopefully this helps others in the future and hopefully I figure out the reason for the code.

So, go figure, as soon as my truck hits 200k I throw a stupid p0300 code. Luckily I have a ScanGauge and was able to read it immediately.

Platform

1999 Toyota 4Runner -Auto - 3.4L V6 - 5vz fe

Symptoms

The truck has been having a weird/rough-ish idle in the morning (garage kept) but never hesitates to start. After about 5-10 seconds it begins to idle normal. When I head out to work and get going on the road (30mph+) it wants to stumble a little under throttle. Very similar to the stumble you get when you start to run out of gas but not as drastic/jerky (I know this feeling first hand lol). After about 5 min of normal driving, it drives fine. I can even turn the truck off and start it back up a few minutes later and everything is fine, with normal driving. As a side symptom I've noticed a gas smell in the oil, but it's not necessarily running rich (at least not till maybe recently)

Possible Causes

Spark Plugs - The plugs are around 6k old. No issue then. Plugs are spec. Old plugs dirty but not fouled.
Wires - The wires are probably around 50k old. Wires are spec.
Injectors - Unknown Status
MAF - Last cleaned roughly 30k miles ago
Throttle Body - Last cleaned roughly 30k miles ago
Intake - New Airiad MIT roughly 2k miles old.

Recent Maintenance

Oil Change
Oil Filter Change
New Air Filter
New Valve Cover Gaskets

Troubleshooting

Inspect Spark Plugs for fouled plug due to possible faulty injector.

Inspect Wires

Inspect MAF

Inspect Throttle Body

Initial Guess Before Troubleshoot

If I had to take a stab at the possible cause of the problem my initial thought is faulty injector. This would cause the intermittent short rough idle and also cause the stumble. Likely by dumping too much fuel into the system. This would also make sense of why the oil has a gas smell to it.


Other's thoughts?

Update:

Engine lost most of it's compression and power while driving home one evening. Limped it home and replaced the engine after some time. Upon inspection of old engine, once out, #3 cylinder was completely washed (with coolant) revealing complete head gasket failure. This would explain symptoms and the misfire codes. After engine sat for a period of time (over-night), coolant was allowed the penetrate into the cylinder, causing the misfire to happen upon startup.

I believe with these vehicles it's possible to detect early headgasket failures with the geeric P0300 code. If you get this code and do not suspenct any issues with the common parts (spark plugs, wires, injectors, etc) it would be very worth while to get a leak-down or compression test done. This is a fail-proof way to confirm headgasket failure at an early stage before it can completely ruin any internals.

If you are getting mutliple codes for misfiring, the P0300 as well as a specific cylinder misfire, it's a very good indication that your engine is experiencing signs of headgasket failure at the point to where internal components have been compromised. A compression test or leak-down test is highly reccommended at this point. Engine replacement is likely the best option as at this stage the block, valves, and other internal components have likely been compromised and rebuild would be far more expensive and time consuming.

[Toyotayoda]

Helps when the misfires are cylinder specific, but no matter, probably have an bad fuel injector. You're at the right mileage, and age, I've known these injectors to fail in the manner you're describing before. You should check fuel pressure, and move ignition coils and plugs around to see if the misfire moves with any of that, just to be absolutely sure.

[LittleCaesar]

+1 on the injector. Possibly leaking. Short of being able to see their pulse rate with a nice scantool I'd grab a DVM and ohm them out. You may get lucky and find one just barely out of spec.

[SCHUNTER1969]

So what you're saying is that you should just let your car warm up before driving to work!

Have you ever replaced your fuel filter? I know Toyota will tell you that is a life time part but that was before they started putting all this BS in gas.

Have you ever replaced your PCV valve?

Also a thought, you could flush your gas intake with sea foam! I did this at 200k, I waited until my gas light came on and then some. When I guestimated I had about 2 gallons left I put 3 cans of sea foam in the gas tank. I let my 4runner idle in the drive way for about 30 minutes, revved the engine a couple times and shut the engine off. I let it sit for another 30 minutes allowing the sea foam to sink into any carbon built up. And then I started the 4runner again and let it idle until it ran out of gas. Once it ran out of gas I replaced the fuel filter, PCV valve, oil change, spark plugs, etc. It was a fun day.

My point being, you have done some maintenance but there is still a lot you did not list completing.

If you can't narrow down which cylinder is misfiring, the guessing game for fuel injectors is going to get expensive. At 190k, I was driving home and one of my fuel injectors just completely crapped the bed without any prior symptoms of failure. I woke up the next morning to go have my CEL read to see which cylinder was misfiring and my car drove fine. Then two days later it crapped the bed permanently, left real bad crap stain. Thankfully it was on my passenger side.

[symlink]

Personally here what I would do because it sounds like its in need of some maintenance.

Get a can of Seafoam and seafoam it (youtube videos will help if you don't know how)
Replace plug wires/make sure you have the right spark plugs
Replace the Fuel filter
Buy a can of the CRC MAF cleaner and do that (be careful to not strip the screws when trying to take it out)
Clean the throttle body

After this if none of this helps or reduces the symptoms depending on the 4runner if its the CA model that has two cats you can look into the injectors or it could possibly be that Air fuel ratio sensor. I know when I replaced mine alot of my problems went away.

[JWaldz]

Originally Posted by LittleCaesar

+1 on the injector. Possibly leaking. Short of being able to see their pulse rate with a nice scantool I'd grab a DVM and ohm them out. You may get lucky and find one just barely out of spec.

I can do that.. Not sure how accurate it will be though. They're likely all working, because I don't have a bad misfire or anything. Nor have I thrown any other codes. However, I think one is on the way out.

Originally Posted by SCHUNTER1969

So what you're saying is that you should just let your car warm up before driving to work!

Have you ever replaced your fuel filter? I know Toyota will tell you that is a life time part but that was before they started putting all this BS in gas.

Have you ever replaced your PCV valve?

Also a thought, you could flush your gas intake with sea foam! I did this at 200k, I waited until my gas light came on and then some. When I guestimated I had about 2 gallons left I put 3 cans of sea foam in the gas tank. I let my 4runner idle in the drive way for about 30 minutes, revved the engine a couple times and shut the engine off. I let it sit for another 30 minutes allowing the sea foam to sink into any carbon built up. And then I started the 4runner again and let it idle until it ran out of gas. Once it ran out of gas I replaced the fuel filter, PCV valve, oil change, spark plugs, etc. It was a fun day.

My point being, you have done some maintenance but there is still a lot you did not list completing.

Originally Posted by symlink

Personally here what I would do because it sounds like its in need of some maintenance.

Get a can of Seafoam and seafoam it (youtube videos will help if you don't know how)
Replace plug wires/make sure you have the right spark plugs
Replace the Fuel filter
Buy a can of the CRC MAF cleaner and do that (be careful to not strip the screws when trying to take it out)
Clean the throttle body

After this if none of this helps or reduces the symptoms depending on the 4runner if its the CA model that has two cats you can look into the injectors or it could possibly be that Air fuel ratio sensor. I know when I replaced mine alot of my problems went away.

I have replaced the fuel filter. Probably around 40k miles ago. I've never seafoamed so I'll definitely look into that. Haven't replaced or inspected the PCV. I'm hoping to find a fouled spark plug. If not, I will keep digging.

[JayRolla]

Originally Posted by JWaldz

I can do that.. Not sure how accurate it will be though. They're likely all working, because I don't have a bad misfire or anything. Nor have I thrown any other codes. However, I think one is on the way out.





I have replaced the fuel filter. Probably around 40k miles ago. I've never seafoamed so I'll definitely look into that. Haven't replaced or inspected the PCV. I'm hoping to find a fouled spark plug. If not, I will keep digging.

A bad plug, wire or coil can cause the misfire. Fuel is not burnt so it gets in gas. Like stated start with basics.

What sucks is if it is an injector without completely failing could be hard to track down. Test them for resistance.

[Coopsdaddy]

I'm having the exact issue but mine is showing #5 cylinder.

[mmendelscfi]

I would eliminate "spark" as the issue first. Because it's easiest.

Noted that you changed plug wires. Did you also change the plug boots under the coil packs?

We chased misfires for quite a while and neglected the boots under the coil packs. after replacing those we finally eliminated the mis-fires.

We finally noticed some carbon tracking on a plug and that was what pointed us to the boots under the packs. It's easy to miss as the tracks are quite faint.

[maclean216]

I'd try coil packs. I was having similar issues @ 260,000 miles. Changed out fuel injectors, plugs, and wires. Problem continued until I put in new coil packs. Just FYI.
Good luck.

[calicojax]

Any results?

[JWaldz]

Originally Posted by calicojax

Any results?

Was wanting to try and tackle it over my Thanksgiving 4 day weekend but I never got the time. The free time I did have the truck was hot and not really a pleasure to work on when hot haha.

I haven't gotten the code since that one day, and the symptoms have seemed to dissipate. Gonna be interesting once I do find out what the deal is.

[JWaldz]

Threw a P0303 this morning which indicates a misfire in cylinder #3. This was sort of what I was waiting on so I wasn't chasing a wild goose. Now I know which cylinder to look at. Plan to hop on this soon.

[LittleCaesar]

My money is on the injector. When electrical issues (wires, coils, etc) are the culprit of a misfire, via my own experiences, they usually don't ever remedy themselves until replaced.

[JWaldz]

Originally Posted by LittleCaesar

My money is on the injector. When electrical issues (wires, coils, etc) are the culprit of a misfire, via my own experiences, they usually don't ever remedy themselves until replaced.

I'm almost certain is it.. I'm likely going to just pull every single one and send them off to be cleaned. I just did valve cover gaskets not long ago too