Audi S3 misfire


New Member
Jan 23, 2022
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Hi there, I am new to this and not sure if I’m even in the right section. I’m after any kind of help really as I’m now Losing my mind. I have an Audi S3 2008 with a misfire on cylinder 3 with a code of po303 and occasionally I get code PO171. I have changed so many things and had bits off trying to find the fault causing this. I’ve done a lot of research via this forum also seen the one about the spark plugs possibly being wrong as it has a stage 1 map so I have changed those but to no avail. She starts up very lumpy with recs sitting around 1200 and sounds like a very worn out diesel, once the revs drop she sounds a bit better but is still lacking in power and occasionally she will hold back and then go again. Sometimes she runs okay other times not so. Over the last few weeks I have changed the…

inlet, spark plugs, I’ve swapped the coil pack around, pcv valve, oil filter housing, had all the injectors out and cleaned them, new pipes for the pcv valve, I’ve done the carb cleaner trick for vacuum leaks and found nothing. I’m sure I’ve done more but I’m just so frustrated at the moment I can’t think. Can anyone come up with any ideas and what to check? I’m going to do a compression check hopefully in the next few days.
Any ideas at this moment would be very much appreciated