Confusing code state
 

I had two cylinders(1 and 4) misfiring about 2 months ago. The engine lost power - violent vibrations - and check engine light flashing. I changed the two coilpacks - and the car was fine.

Now the check engine light has come on again. I read the codes at Autozone ... P0300, P0301, P0302, P0303, P0304 and P0171. How can all the cylinders be misfiring when the car is running just fine? There is a slight vibration (like knocking) at low RPMs ... but the engine is performing absolutely fine. I tried driving at quick accelerations several times today - and the pickup is perfect!

The guy at Autozone said the P0171 might have come on just because of the other codes.

Just to make clear, the check engine light is STILL now, not flashing like before.

Anyone had this situation before? Your ideas would be very helpful. Thanks!

RE: Confusing code state
 

your plugs could be bad or misgapped

RE: Confusing code state
 

Update ... I switched coils 1 with 2, and 3 with 4. I did that because 1 and 4 are new ... 2 and 3 are old and looks cooked. I thought maybe the engine will complain/vibrate violently. Nothing like that ... I'll change the two old coilpacks tomorrow.

If it is the plugs ... that's something new for me and I'll have to read up before I attempt to change. But how can I be sure? The codes are just saying that cylinders are misfiring.

Another thing I noticed today, if I leave the engine running for a while, the RPM drops low at times - and ONLY THEN the check engine startsFLASHING for a 10-15 seconds ... then the RPM picks up and the check engine light becomes STILL.

Any ideas?

RE: Confusing code state
 

misfiring... change your sparkplugs

RE: Confusing code state
 

Your car's misfiring and It's either 1 or more of your coils. I've seen this all of the time when yourcheck enginelight flashes Get your car scanned and see which cylinder it is.

RE: Confusing code state
 

The code says that all 4 are misfiring ... but the car runs surprisngly better than expected. Almost no problem other than the slight vibration at low RPMs only.

I have already changed the 4 coilpacks - and nothing have changed. I could try to change the sparkplugs as well - but how can I be sure that is the problem?

RE: Confusing code state
 

Did you fix the code p0171(System too lean bank 1)? You have a vacuum leak somewhere. Start your car and listen for any leaks or what I do is spray brake cleaner on all da hoses. The car will run rough once you hit the leak.
What is the ENGINE, MODEL, and YEAR?

RE: Confusing code state
 

Thanks, AudiTech. It's a 2003 A4 1.8T Tip ... mileage running 65K now.

Yes, I was thinking about a leak too ... because if I leave the car running with the hood open, I hear a hissssing sound somewhere, but didn't find any obvious leaks anywhere. By a vacuum leak, do you mean a leak in the combustion system?