P0300 Fixed, Finally!

Hi Everyone,

I've never had an account or posted here before but after success finding the cause of the P0300 code on my Almera today, I thought I'd make an account and post the fix.

My Almera is an N16 1.8 Sport (QG18DE with VVT).

Driving back from Cornwall back in August, my car started misfiring and the check engine light came on, not flashing, just lit up constant. OBDII scanner just shown 'P0300', nothing else.

I noticed the following symptoms along with that:
  • Bad jerking when accelerating. I can only describe it as the engine would feel like it completely lost power for a second then back up to normal revs, and keep doing it.
  • The jerking seemed to get better the higher the revs, whether it was just less noticable at higher revs or not I don't know.
  • It would worsen when I changed up a gear and the revs dropped.
  • Idle was ~1100RPM when cold, ~750 when warmed up.
  • Timing advance was random. (e.g. 7° then -4° then 8° then -2°).
  • The rev counter needle would keep dipping then return to normal.
  • Consuming far more petrol than usual.
I got hold of the N16 service manual and looked in the P0300 section and followed most of the things there to try and get to the bottom of it. These are the things I tried:
  • New coil packs (Good deal on them luckily).
  • New spark plugs (NGK BKR5E-11). Old plugs looked OK but new ones are cheap enough to swap out and try anyway.
  • Checked MAF. Sensor seemed nice and clean. Air flow rate was within spec.
  • Oxygen sensor voltages within spec.
  • Checked air filter.
  • Removed air intake (after MAF), sprayed throttle body cleaner in throttle body as per instructions.
  • Used a ghetto DIY smoke machine (hose pipe + nitrile glove + jubille clip + ecigarette) to blow smoke into intake with engine off. No leaks.
  • Mine doesn't have an EGR valve so not that.
  • 'Power balance test' by disconnecting the harness to each injector and listening for RPM drop. RPM dropped when each one unplugged.
  • Checked injectors were clicking when engine running.
  • Checked injector harnesses were putting out battery voltage.
  • Built-in fuel filter so didn't think that would be it.
I'll be honest, I was starting to get pissed off and thought it must be the timing chain. I was sick of looking online about P0300 and the MANY possible causes! My car drinks a fair bit of oil (always has done since I bought it 5 years ago). I thought that plus timing chain, it was probably time to say goodbye.

But today, I was just about to start taking the rocker cover off to look at the timing chain tensioner distance and thought, what about the cam shaft sensor?

I removed the cam shaft sensor, cleaned it up (had some small metal filings on it and dirty oil), and popped it back in. Started it up and idle was fine again. Took her for a spin and misfire completely gone!! Cleared code and hasn't come back so far. Engine pulling smooth.

I just thought I'd share this with you all just incase you get the same issues as me and struggle to find any answers.

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