2008 BPY misfire at idle
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2008 BPY misfire at idle
Hello! A few weeks ago I got an A3 with a bad slave cylinder. Dropped the trans, replaced the slave cylinder, and when I put everything back together the engine started misfiring (at idle) on cylinders 3 and 4 (according to the OBDII scanner that I borrowed). I replaced the plugs and coils and it's still misfiring. What's the next thing to look at? I inspected the rubber diaphragm inside of the PCV valve and it seems intact. The engine sounds fine when you give it some gas but it runs shaky at idle.
I am going to get my hands on that scanner again tomorrow and see what it tells me, but I anticipate that it will be the same story as before. Before I changed the coils I moved them around and it caused cylinder 1 to start misfiring too, but it didn't move the misfire off of cylinders 3 and 4.
Thank you for any and all help y'all can provide.
P.S. Is there maybe a ground or something that I might have missed while removing/installing the transmission? It was idling fine before I fixed it.
I am going to get my hands on that scanner again tomorrow and see what it tells me, but I anticipate that it will be the same story as before. Before I changed the coils I moved them around and it caused cylinder 1 to start misfiring too, but it didn't move the misfire off of cylinders 3 and 4.
Thank you for any and all help y'all can provide.
P.S. Is there maybe a ground or something that I might have missed while removing/installing the transmission? It was idling fine before I fixed it.
AudiWorld Senior Member
Joined: Nov 2023
Posts: 741
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From: Sweden
Did I get this right?
When the misfiring started:
1. You bought 4 new ignition coils and 4 new plugs without troubleshooting?
2. You wrote: "Is there maybe a ground or something that I might have missed while removing/installing the transmission?" but you have not investigated into that?
When the misfiring started:
1. You bought 4 new ignition coils and 4 new plugs without troubleshooting?
2. You wrote: "Is there maybe a ground or something that I might have missed while removing/installing the transmission?" but you have not investigated into that?
Thread Starter
AudiWorld Junior Member
Joined: Mar 2026
Posts: 6
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Did I get this right?
When the misfiring started:
1. You bought 4 new ignition coils and 4 new plugs without troubleshooting?
2. You wrote: "Is there maybe a ground or something that I might have missed while removing/installing the transmission?" but you have not investigated into that?
When the misfiring started:
1. You bought 4 new ignition coils and 4 new plugs without troubleshooting?
2. You wrote: "Is there maybe a ground or something that I might have missed while removing/installing the transmission?" but you have not investigated into that?
2. I did not immediately consider a missed ground until around the time I was making the post. My next step is to put the car back up on stands and get under it and see if I can't see anything egregious. Is there anything that is "easy to miss" that comes to mind?
I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along. Thanks for your response and and additional information or thoughts on what to look for.
AudiWorld Senior Member
Joined: Nov 2023
Posts: 741
Likes: 88
From: Sweden
When you replaced all perfectly working coils (before the slave cylinder swap) with four new presumably working, did you clean the spark plug tubes and check for moisture in them?
Since the original ignition coils worked and there is no way a mechanical work under your car can affect any of your ignition coils just like that, I'd replace the new with the original. I'd let the plugs stay.
While you do that, check as previously mentioned, moisture, cable damage and dirt.
You wrote "I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along". Ok, good but you don't have a scanner. Yet you can easily afford to replace spark plugs and coils that are not even broken?
Explain that car philosophy to me.
Since the original ignition coils worked and there is no way a mechanical work under your car can affect any of your ignition coils just like that, I'd replace the new with the original. I'd let the plugs stay.
While you do that, check as previously mentioned, moisture, cable damage and dirt.
You wrote "I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along". Ok, good but you don't have a scanner. Yet you can easily afford to replace spark plugs and coils that are not even broken?
Explain that car philosophy to me.
Last edited by JohnnyJ; Mar 12, 2026 at 07:49 AM.
Thread Starter
AudiWorld Junior Member
Joined: Mar 2026
Posts: 6
Likes: 0
When you replaced all perfectly working coils (before the slave cylinder swap) with four new presumably working, did you clean the spark plug tubes and check for moisture in them?
Since the original ignition coils worked and there is no way a mechanical work under your car can affect any of your ignition coils just like that, I'd replace the new with the original. I'd let the plugs stay.
While you do that, check as previously mentioned, moisture, cable damage and dirt.
You wrote "I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along". Ok, good but you don't have a scanner. Yet you can easily afford to replace spark plugs and coils that are not even broken?
Explain that car philosophy to me.
Since the original ignition coils worked and there is no way a mechanical work under your car can affect any of your ignition coils just like that, I'd replace the new with the original. I'd let the plugs stay.
While you do that, check as previously mentioned, moisture, cable damage and dirt.
You wrote "I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along". Ok, good but you don't have a scanner. Yet you can easily afford to replace spark plugs and coils that are not even broken?
Explain that car philosophy to me.
I do need to buy my own scanner asap. Do you have any recommendations for a stand-alone wired scanner?
I was incorrectly treating the misfire as a new problem, and I need to get under there and make sure I didn't miss anything, but I'm not sure what it would be.
Last edited by thesuave; Mar 12, 2026 at 08:54 AM.
AudiWorld Senior Member
Joined: Nov 2023
Posts: 741
Likes: 88
From: Sweden
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Thread Starter
AudiWorld Junior Member
Joined: Mar 2026
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When you replaced all perfectly working coils (before the slave cylinder swap) with four new presumably working, did you clean the spark plug tubes and check for moisture in them?
Since the original ignition coils worked and there is no way a mechanical work under your car can affect any of your ignition coils just like that, I'd replace the new with the original. I'd let the plugs stay.
While you do that, check as previously mentioned, moisture, cable damage and dirt.
You wrote "I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along". Ok, good but you don't have a scanner. Yet you can easily afford to replace spark plugs and coils that are not even broken?
Explain that car philosophy to me.
Since the original ignition coils worked and there is no way a mechanical work under your car can affect any of your ignition coils just like that, I'd replace the new with the original. I'd let the plugs stay.
While you do that, check as previously mentioned, moisture, cable damage and dirt.
You wrote "I am operating with Basic+(™️) automobile repair knowledge, learning this car as I go along". Ok, good but you don't have a scanner. Yet you can easily afford to replace spark plugs and coils that are not even broken?
Explain that car philosophy to me.
Just now I got a cheap OBDII reader and cleared all codes and started the car. The car idled rough but did not cause the check engine light to come on, and no codes thrown to the reader. I put the old coils back on and it pretty quickly threw codes for "random/multiple cylinder misfire" as well as codes for cylinders 1, 3, and 4. The idle was rough and jumpy at around 1k RPMs. I cleared the codes and put the new coils back in, and the idle is rough and low, at around 500-750 RPMs, but again no check engine light and no codes.
I did not get under the car yet but from what I can see from up top all electrical connections and grounds are in place.
Is there something electronic that I need to reset? The battery was removed when I dropped the transmission to do the slave cylinder.
Last edited by thesuave; Mar 12, 2026 at 06:03 PM.
AudiWorld Senior Member
Joined: Nov 2023
Posts: 741
Likes: 88
From: Sweden
Before the slave cylinder issue, were you truly observant how the motor idled? Maybe it was rough before as well but you didn't notice?
Is the car low on gasoline? If so, fill it up and drive for a while. Is the idle better when the motor has reached working temperature?
Also, borrow a decent reader and check again.
Is the car low on gasoline? If so, fill it up and drive for a while. Is the idle better when the motor has reached working temperature?
Also, borrow a decent reader and check again.