Troubleshooting The P0300 Code: Slight Stumbles - Rough Idles - Hesitations

[LittleCaesar]

Curious as well. I still think your ride hated being stuck in that Arkansas gorge or stream some years back and is exacting revenge on its driver.

 

[JWaldz]

Did you ever sort this out?

Curious as well. I still think your ride hated being stuck in that Arkansas gorge or stream some years back and is exacting revenge on its driver.

I did get it fixed up but I'm monitoring it as of right now. I had 6 OEM injectors pulled from a local yard here and had them sent off to be professionally inspected, rebuilt/cleaned. Got them back and swapped them in. Also redid my valve cover gaskets as it was apparent they were leaking at the back (due to me not using any FIPG per the manual).

The spark plug on Cylinder #3 (where the misfire was) was not fouled and in fact, still look new (less than 20k miles on it anyways). The wire to number 3 coil pack was a little dirty as was the coil packs contact point. I cleaned them both up the best I could and put #3 coil pack at the #1 cylinder position.

As of right now, the start up is normal and no longer giving me issues. If after time It begins to do the same thing I'll know for a fact it's not the injectors. If it's cylinder #3 misfire it's the wire and if it's cylinder #1 misfire it's the coil pack. I think I'm due for new wires at this point anyways, so I plan to order a set soon.

I still think your ride hated being stuck in that Arkansas gorge or stream some years back and is exacting revenge on its driver.

lol, the elevation definitely plays a roll in it's every day behaviors now. I rarely ever got over 3k on the tach down south. Here, it's an every day occurrence.

 

[LittleCaesar]

At least it is the easy stuff so to speak. When my Denso replacement wires went south on me last Jan due to a hole in the #4 boot I replaced the wires with OEMs that can sometimes be found on Amazon for $40. Also replaced that coil and have had no problems since then.

 

[Clovertucky]

intermittent miss #4

I had a cel indicating an intermittent miss on #4. When i changed the plugs and wires, I found a broken wire end. The boot shows some arcing. Plugs had 35k
on them, i think the wires were original. All issues seem resolved.
Sorry, having trouble sending pics.
Dick

 

[JWaldz]

Well I got a rough start up this morning and a couple codes, P0300 & P0303 is back

Unfortunately, I think it's the worst case scenario at this point.

So far:
- Replaced Injectors
- Replaced Plug Wires
- Swapped #1 and #3 Cylinder Coil Packs
- Check #3 Spark Plug (looks new)

So my next guess is burnt valve. I'm going to switch around spark plugs first, then I guess if that doesn't fix anything I'll have to look into a valve job.

:moping:

 

[catrains]

my guess with the miles is fuel pressure issue. check so its proper before you spend more $$$.

 

[JayRolla]

Well I got a rough start up this morning and a couple codes, P0300 & P0303 is back

Unfortunately, I think it's the worst case scenario at this point.

So far:
- Replaced Injectors
- Replaced Plug Wires
- Swapped #1 and #3 Cylinder Coil Packs
- Check #3 Spark Plug (looks new)

So my next guess is burnt valve. I'm going to switch around spark plugs first, then I guess if that doesn't fix anything I'll have to look into a valve job.

:moping:

Compression check and leak down test. Maybe have fluid analyzed. Good luck.

Thinking about it usually of a burnt valve you will constantly have an issues. Usually at WOT and higher rpm. Get a major stutter/misfire. I also never got a cel since coil plug and injector was all firing. Different vehicle though.

 

[JWaldz]

Compression check and leak down test. Maybe have fluid analyzed. Good luck.

Thinking about it usually of a burnt valve you will constantly have an issues. Usually at WOT and higher rpm. Get a major stutter/misfire. I also never got a cel since coil plug and injector was all firing. Different vehicle though.

Compression test is next on the list.

It's a very weird situation. I did a block test a few weeks ago and it came back normal. I dunno what is up with this thing. But will keep troubleshooting.

It drives normal once it gets past the rough-ish start.

Could a belt or pulley issue cause a misfire in a specific cylinder? I'm getting some nice screeching in the morning along with the (sometimes) "water faucet" noise. Clears up after only a few seconds, but it's worth mentioning.

 

[808HI4Runner]

How is your 4Runner now? I am experiencing similar issue.

 

[JWaldz]

How is your 4Runner now? I am experiencing similar issue.

I was driving home one evening and the engine almost completely let up. It was losing compression, backfiring, and stumbling. Long story short, I ended up replacing the engine. Took the old one apart and it revealed that #3 cylinder was completely washed with coolant due to headgasket failure.

My best advice, do a leakdown and compression test if you've crossed off all other possible causes.

 

[RoxToy00]

scary, not good, seeing similar issues (slow to start, ruff running under acceleration regardless of speed when cold or warm), P0300 intermittently and P0301 regularly (P0171 cleared up with MAF cleaning). I have all new plugs wires coils boots injectors to throw at my '00 V6 auto 4runner that has 240K miles and what i am finding to be a "sketchy" maintenance history. Blown HG would be catastrophic for this very clean no rust Runner.

 

[99 Silver]

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.

This seems to be Exactly what the wifes 99 is doing. We got it just over a year ago it 267k and now its it 280k. It was idling rough at cold start and "smoking" at startup, then threw p0300 and p0303 starting about a week ago... Then p0302 joined the party! I was going to rent a compression tester from kragen(I still call it that) when I first decided to pull plugs and stick my $40 endoscope in there. I did it on a cold engine and found a nice lil puddle in cyl 3! Yaaay! So yesterday I rented a block tester instead. The fluid turned barely blue green but its there. It seems like when the block cools is when the coolant is able to leak into that cyl.

I do most repair and as much maintenance as I can as a home mechanic but... My Tools and rebuild experience are minimal.

My "question" is, since it seems like its just starting to fail, is it worth it to have it "rebuilt" or should I just get an already rebuilt one and have it installed? I will be getting quotes this coming week...

TIA ALL!

 

[JWaldz]

This seems to be Exactly what the wifes 99 is doing. We got it just over a year ago it 267k and now its it 280k. It was idling rough at cold start and "smoking" at startup, then threw p0300 and p0303 starting about a week ago... Then p0302 joined the party! I was going to rent a compression tester from kragen(I still call it that) when I first decided to pull plugs and stick my $40 endoscope in there. I did it on a cold engine and found a nice lil puddle in cyl 3! Yaaay! So yesterday I rented a block tester instead. The fluid turned barely blue green but its there. It seems like when the block cools is when the coolant is able to leak into that cyl.

I do most repair and as much maintenance as I can as a home mechanic but... My Tools and rebuild experience are minimal.

My "question" is, since it seems like its just starting to fail, is it worth it to have it "rebuilt" or should I just get an already rebuilt one and have it installed? I will be getting quotes this coming week...

TIA ALL!

Sorry for the late reply, I don't frequent here as much anymore!

Depends how long the leak has been going on for. Coolant is very hard on engine internals, obviously. It's hard to know what's been compromised until it's been disassembled.

I know that's not much of an answer, but it's honestly a case by case situation and how much time and money you want to invest in it.

I think I kind of knew what my issue was at some point, and at that point it was beyond repair. So, I rode out the engine as long as possible until it completely have out.