Codes P0105 and P0300?

Tiny
RAMJACCORP
  • MEMBER
  • 2002 MAZDA MILLENIA
  • 2.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 21,700 MILES
I've been told this is the hardest car in the world to work on, and after trying, I have to agree. Error code P0105 came up, after the car started idling rough. I tested the MAP/boost sensor and its companion solenoid, disconnected and cleaned all electrical contacts, cleaned MAF sensor, etc. There are hoses that I couldn't access under the air intake pipe (couldn't get that thing off!), But the mileage is so low, the vacuum hoses all look pretty new. After putting everything back together, I got a new code: P0300. Both codes point to any one of about 15 or more causes. I have readings from a basic code reader, if they're of any use. One thing that stands out: a reading of 25 on the short-term fuel trim - I know that's way too high. Also, the O2 readings seem really low. I have no money for expensive testing at a shop, so I'm pretty screwed. The only symptom so far is very rough idle. I haven't driven it since the CEL came on. Any thoughts? Thanks for your time and any help you can offer!
Wednesday, May 1st, 2024 AT 3:22 PM

13 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

If the short-term fuel trims are +25%, you must have a somewhat significant vacuum leak, weak fuel pump, or an exhaust leak pre cat.

If you haven't already, check the fuel pressure to confirm it is within the manufacturer's specifications.

Here is a link that explains how to check:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I attached the pressure specifications below (pic 1). The remaining pictures are the step-by-step diagnostics for the P0105 code.

Let me know if this helps.

Take care,

joe

See pics below.

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Thursday, May 2nd, 2024 AT 7:36 PM
Tiny
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Thanks so much for the advice and hard-to-find documentation, Joe! I'm not sure I can tackle your recommended tasks, partly because the car is such a beast to work on, and partly due to my skill level. I do have one crucial question: Yesterday, testing for vacuum, I removed the hose from the MAP sensor solenoid that feeds under the intake pipe I couldn't remove. (There are several hoses fed in there, with plastic tees that I hear are prone to failure). I felt very slight vacuum, but when I plugged the end with my finger, I heard a significant hiss. I'm guessing that's a sign of that major leak you referred to, and not a normal occurrence, right? Since I can't get that intake pipe off without dismantling half the engine, I was thinking about just cutting the hoses, one by one, and pulling them out, then feeding in replacement hoses and tees. Of course, it might not be the hoses or tees at fault. I'm not comfortable spraying carb cleaner all over that really hot-running engine to try and find the source of the leak.
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Friday, May 3rd, 2024 AT 8:45 AM
Tiny
JACOBANDNICKOLAS
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Hi,

That is exactly what it sounds like. If you are able to reconnect the new hoses, that would be a good idea. See if you can narrow down where the sound comes from.

Let me know if you do it and the outcome.

Take care,

Joe
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Friday, May 3rd, 2024 AT 7:05 PM
Tiny
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Time for an update, and another question. Had a smoke test done, and sure enough, the vacuum leak seems to be in that area I described that I can't access. I started to dismantle some parts again, and when I removed the Charge Air Cooler, I found a small amount of very strong, foul-smelling oil inside the pipes, and the rubber hose that connects it to the supercharger air pipe that I couldn't remove. I hope I'm wrong, but I have a feeling there shouldn't be oil of any kind in there. Thoughts? I'm holding off on the disassembly, because I might not be able to find replacement gaskets for the old girl.
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Sunday, May 12th, 2024 AT 3:39 PM
Tiny
JACOBANDNICKOLAS
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Hi,

There really shouldn't be oil in there. I'm wonder if that is getting past the SC. Was there anything that appeared to be leaking that you could see?

Let me know.

Joe
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Sunday, May 12th, 2024 AT 6:33 PM
Tiny
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Thanks for the reply, Joe. From above, I see no leaks anywhere. Nice and dry. Nothing on the ground, but I haven't inspected the engine's underside. Will try to do that tomorrow.
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Sunday, May 12th, 2024 AT 7:13 PM
Tiny
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JACOBANDNICKOLAS is one of our best! Please let us know.
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Tuesday, May 14th, 2024 AT 10:17 AM
Tiny
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I inspected the engine, and there's no visible oil leaks. Also, I did some more research, and got some conflicting info. I saw several people say that a small amount of oil in the pipe is completely normal, as it is condensed oil vapor. I found less than a teaspoon of oil, so I'm hoping that this falls under the "normal" classification. The only thing left to do now is disassemble enough to visually inspect the area where the vacuum leak appears to be coming from. That's another dilemma, as I haven't found decent instructions on how to do that yet. Here's the area where the leak seems to be coming from.
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Tuesday, May 14th, 2024 AT 10:33 AM
Tiny
JACOBANDNICKOLAS
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Hi,

First, I would say yes to the amount of oil found is acceptable. As far as the leak, I just pulled out the manuals and it shows a P model and an S model. Both are the v6, but neither are showing a turbo.

The pipe you are referring to appears to have two bolts at the rear of the engine and then both ends would be clamped. Is that what you are seeing?

Also, let me know if the model millennia you have.

Joe
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Tuesday, May 14th, 2024 AT 6:22 PM
Tiny
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Hi Joe, thanks for confirming the small piece of good news regarding the oil. Strange about the manuals. The S model designates the turbocharged version. Mine is a 2002 S. From what I've been able to find online, if I'm not mistaken, the engine is designated in manuals as "KJ." The non-turbo model is "KL."

The large pipe is indeed the one clamped at both ends. There are several other bolts toward the firewall, as well as 2 bolts hidden underneath the pipe, which I was able to remove. I read somewhere that you have to remove an entire section as one unit, because the various parts are interconnected with hidden, inaccessible bolts. I sadly had the misfortune of confirming that. Here's a photo showing the parts involved. Getting all of that removed seems to be the only way to inspect the hoses and tees, as well as look for cracks causing the leak. Fun, huh?
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Tuesday, May 14th, 2024 AT 7:29 PM
Tiny
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Hi,

Fun? I'm glad you're doing it and not me. LOL You have to wonder who comes up with these designs.

Regardless, let me know how things work out for you.

Joe
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Wednesday, May 15th, 2024 AT 7:49 PM
Tiny
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I managed to disassemble the necessary parts and remove everything as one unit, and sure enough, I found one buried plastic tee had been burnt up. The hoses looked fine, so I replaced all the plastic tees I could find (3) with metal ones and put it all back together. Not a job I'd recommend, but I got it done somehow. Haven't had a chance to drive it yet (whole 'nuther long story), but it started up and ran without throwing any codes so far.
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Wednesday, May 29th, 2024 AT 8:16 AM
Tiny
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Hi,

Thanks for the update. I'm glad that nightmare is over for you. LOL

Good job, and feel free to come back anytime in the future.

Take care,

Joe
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Wednesday, May 29th, 2024 AT 7:55 PM

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