2005 Intermittent P0303 Check Light : Cyliner 3 Misfire

[madcheeku]

I got a 90303 error code on my 2005 legacy gt about couple of weeks back. That's most commonly cylinder 3 misfire.

I did a reset to confirm if the check light went on for other reasons and it came back about a week later with the same error code.

Now the light seems to turn on and off intermittently. Is there a fuel injector cleaner or something I can try before going to the mechanic? Is there anything else I can try?

I have about 80K on my car.

[Dookie]

Here's a few things to check when you get a misfire code.

1) Try a fuel injector cleaner & fresh new tank of gas.
2) Faulty spark plug, change plugs
3) Disconnected or loose vacuum hose, in front & behind intake manifold.
4) Faulty coil pack, test the coil pack by swapping it with another cylinder coil pack. If the code pops up on that cylinder then you know that coil pack is bad.

Good luck

[madcheeku]

Thanks. Any recommendations for fuel injector cleaner?

[TSi+WRX]

^ A lot of us use Techron.

As a corollary to Dookie's excellent ideas, for #1, you can also swap the injectors with another cylinder's, to see if it's the injector that's faulty.

If it's persistently at one cylinder, it's very likely to be something that you can locate to that cylinder: its coil-pack, it's injector, or its plug.

With 80K only the clock, if you haven't changed the plugs before, it's time to do so. If you've changed the plugs at 60K, it's rather unlikely that you'll see a problem now that wasn't apparent soon after the plug change - nevertheless, it's not out of the realm of possibility.

If you're mechanically proficient, the coil-pack switch-out and injector switch-out procedures are straightforward and very, very easy. Separate these two trouble-shooting procedures into discrete components so that you can logically trace which one fixed the issue. Remember that, sometimes, it may take a bit of driving before the code recurs. If you're seeing it at ~1 week intervals, that's the minimum amount of driving you should do, with the swapped-over coil-pack (and then later with the swapped-over injector) before you come to any conclusions, should you not see a new code (matching the cylinder position that you'd moved the suspect cyl. 3 component to) immediately.

The injector cleaner may work...but the fact that it's recurrent on the same cylinder - cyl. 3 - makes me think that it's the coil-pack, injector, or the plug for that cylinder that's the problem.

[Dookie]

Just a follow up to TSI, it usually takes between 40 - 60 miles of driving before the ECU will flash a trouble code on the dash. After the codes have been cleared previously.