Subaru WRX Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
279 Posts
Discussion Starter · #1 ·
I've been chasing a random misfire code (p0300) since around August of last year and getting nowhere. The really bizarre part is that it ONLY happens within roughly 5 minutes of startup, when the car is cold. Even more bizarre... it didn't happen at all winter long. As soon as the temperature began to consistently stay above 40, it began happening again.

When it happened the first time, I did a bunch of research and learned that there was a known issue with the harness on 09-12 models. Even though my car is a 14 model, I figured I would take a look at the harness anyway, since it was a simple fix. That obviously wasn't it.

I then randomly threw a p0303 code. Great news, I thought... must be the coil pack. Swapped the #3 and #1 packs, cleared the codes, and two weeks later, I once again got a p0300 and p0303 code. Since then, I've consistently thrown the p0300 code about once a week (sometimes two weeks), except for the winter. From November till two weeks ago, I was CEL free. The p0303 code only came on maybe 3 times.

More info: 2014 WRX 5 door, base model.
- Car is stock.
- Replaced spark plugs last spring, at around 70K miles.
- Checked the plugs when this began, they are fine.
- Checked the electrical contacts for the coils and injectors... all good.
- Most of these have occurred with either no actual misfire, or a possible, momentary misfire (rough idle).
- No boost or vacuum leaks.
- No loss of power.
- Brand new battery.
- Car is well maintained.

Before you guys say "go to a damn mechanic..." I've already spoken with two Subaru master techs and an independent mechanic. Everybody said that they would need to be there when it happens. Problem is, I cant exactly loan my car to a tech for 3 weeks. The Subaru guy's basically said there isn't much they can do and that I may have to wait till the problem gets worse before it can be reliably diagnosed.

I'm not really sure where to go from here. Has anybody experienced something similar? I was thinking maybe the crank position sensor is going, but then how does one explain the lack of an issue for the duration of the winter?

I'm really stumped.
 

·
Registered
Joined
·
279 Posts
Discussion Starter · #3 ·
Not yet. I was going to, but then it disappeared for the entire winter. Seems logical that if it was a compression issue, it would have continued to throw the same code through the winter months.
 

·
Water.....sometimes waves
Joined
·
1,612 Posts
Did you do everything in the misfire thread? You did not mention Seafoam.

On a similar note I have had a P0420 code doing almost the exact same thing to me as you mention (since last Fall it comes and goes at odd times and durations.) I have been driving it differently and used Seafoam and it seems to being staying off. Course now that I write this it'll come back on..............
 

·
Registered
Joined
·
279 Posts
Discussion Starter · #5 ·
My apologies, I should have given a bit more information.

I did most of what the misfire thread suggested.
- Checked the grounding issue and did the suggested fix. This was the first thing that I did
- New fuel filter installed September of 17 (shortly after the problem began).
- Cleaned MAF sensor the day I did the fuel filter.
- Ran a few gas tanks with injector cleaner, starting the day I did the fuel filter.
- No vacuum or pre-turbo leaks (no leaks at all).
- I didn't pull the O2 sensor, but I did monitor it through an ODB2 app that I have, and it seems to read normal voltage. No other symptoms related to a bad O2 sensor.
- Checked the coil packs (mentioned that above).
- Spark plugs are good.


PCV blowby is an issue as I've recently pulled the intercooler and TB for a much needed cleaning. That made a positive difference in the way the car runs, but no affect on the code. Also did a seafoam treatment a few days before the intercooler and TB cleaning. To clarify, there wasn't that much oil in there, but there was clear evidence of some blowby. Nothing out of the ordinary given the fact this was the first time it was cleaned and the car has 90K miles.

I cant see it being a damaged crank timing gear. I would surely have other symptoms. The car runs fine.

I have not tried cleaning the cam and crank sensor face. I suppose I'll try that this weekend as I'm doing a few other things anyway.

I suppose it cant hurt to check compression, but it seems logical that if it was a compression issue, it would have been exacerbated by cold weather. I did a cold start at -22F in Jan, and I didn't get a code. I'll try to do a compression test this weekend and see what happens.
 

·
Registered
Joined
·
1 Posts
My apologies, I should have given a bit more information.

I did most of what the misfire thread suggested.
  • Checked the grounding issue and did the suggested fix. This was the first thing that I did
  • New fuel filter installed September of 17 (shortly after the problem began).
  • Cleaned MAF sensor the day I did the fuel filter.
  • Ran a few gas tanks with injector cleaner, starting the day I did the fuel filter.
  • No vacuum or pre-turbo leaks (no leaks at all).
  • I didn't pull the O2 sensor, but I did monitor it through an ODB2 app that I have, and it seems to read normal voltage. No other symptoms related to a bad O2 sensor.
  • Checked the coil packs (mentioned that above).
  • Spark plugs are good.


PCV blowby is an issue as I've recently pulled the intercooler and TB for a much needed cleaning. That made a positive difference in the way the car runs, but no affect on the code. Also did a seafoam treatment a few days before the intercooler and TB cleaning. To clarify, there wasn't that much oil in there, but there was clear evidence of some blowby. Nothing out of the ordinary given the fact this was the first time it was cleaned and the car has 90K miles.

I cant see it being a damaged crank timing gear. I would surely have other symptoms. The car runs fine.

I have not tried cleaning the cam and crank sensor face. I suppose I'll try that this weekend as I'm doing a few other things anyway.

I suppose it cant hurt to check compression, but it seems logical that if it was a compression issue, it would have been exacerbated by cold weather. I did a cold start at -22F in Jan, and I didn't get a code. I'll try to do a compression test this weekend and see what happens.

Have you fixed the problem yet? I'm running into a very similar issue!
 
1 - 8 of 8 Posts
Top