CEL on Cold Starts (P0300)
 

Hey everyone,

So for a few months now I've been getting a CEL (P0300). My only mod is Stillen Gen 3 Intakes. I haven't taken it to the dealer for a couple of reasons, main reason being that I've figured out how to "avoid" it - but not fix it altogether, second reason being that I've read way too many stories about dealerships switching everything blindly without knowing what they're actually doing.

So the strange thing about my case is this: I've figured out that on the first start of the day (or after more than 5 or 6 hours of not using it) if I turn the car on for approx 10 seconds, turn it off, then turn it back on again immediately after, the light wont come one. However, if I turn on the car in the morning or in the afternoon after a while (again, lets say 8 hours) of no use, the light will come on.

Any ideas on what the hell may be wrong?!? Seems like a fairly specific scenario, but so far (locally) no one has been able to give me an answer.

Possible causes
- Faulty spark plug (s)
- Faulty ignition coil (s)
- Clogged or faulty fuel injector (s)
- Intake air leak
- Fuel injectors harness is open or shorted
- Fuel Injectors circuit poor electrical connection
- Ignition coils harness is open or shorted
- Ignition coils circuit poor electrical connection
- Insufficient cylinders compression
- Incorrect fuel pressure


Perhaps a list of what you have tried?

bebenegro,
I know this is a very old post but did you ever figure out what was going on? I am going thru the same thing with my Z and everything that Array pointed out is not the case. I don't know if it was the same thing for you but mine would only come on at cold start; if I cleared the CEL after it was warmed up it would not come back on until the car would have to cycle through a cold start again. Mine, every other cold start causes the issue and it always pops on 40 to 50 seconds after starting when it is starting to idle down.

I know all my components Array listed are good otherwise I don't believe I would have made 406hp at the wheels when I got it re-tuned. I have the Stillen SC kit.

Hey guys, I was in a similar situation as well. Have Stillen Gen 3’s on my Z and while I was tuned on Uprev I started getting P0300 codes randomly, coincidentally after getting a new set of OEM Denso spark plugs. I ended up reaching out to Eugene Turkov in Concord, CA who solely tunes on Ecutek. He reviewed my data logs and was able to eliminate the issue by removing the Uprev tune and retuning me on Ecutek, the DTC is still active if there’s ever an issue so the code itself is not disabled. I haven’t run into the issue since making the switch to Ecutek.

If any of you are still having trouble with the code popping, I’d reach out to him. He’s an Ecutek master tuner so you’d be in great hands, apart from the fact that he also works for NASA. He supports remote tuning as well so don’t worry if you aren’t anywhere near San Francisco, CA. Here’s his website: http://www.infiniticare.com/

Sorry for the delay in response tchertel.

Ive narrowed it down to dirty throttle bodies. My workaround when it starts to happen is I turn on the car for 20-30 secs in the morning, shut off, turn on again, and I never get a CEL. My theory is that the gunk in the throttle bodies seize up after not moving for a while (and they do get absurdly dirty to be honest), causing some airflow fluctuations when starting up. A few seconds after all returns to normal. Whenever this starts I take the car in for throttle body cleaning and the problem is resolved for 2-3 years.

Hope this helps!

So I have a 09 6speed manual with the stillen gen 3. I've been getting p0300 ever since. I replaced fuel pump, spark plugs, coil packs, cam seals, fuel injectors, cleaned out MAFS and throttle bodies, and added a fuel pressure gauge. Still getting a p0300 and bought a smoker unit and couldn't find a leak. 02s look good and catalytic looks good. I stumbled to a weird solution. Push button start to ACC without igniting the engine, wait for 10 seconds and turn on the engine. Do this when the car is cold or haven't ran in 5 hours or so.

This have been working for me for a few months without any issues. If I forget and start the car immediately in a cold start, p300 shows up. I spent enough where I'm not trying to spend any more. I think it may be an ECU problem. It's all stock and no tunning.