Cold Idle Misfire Problem, help wanted please...

[325_bucks]

Sorry for the long post, appreciate anyone reading to give me advice...

Hi all

Imposter here from the M6 side, but that side is quite quiet so I hope you don't mind me asking here as it's going to be relevant to both.

As short as I can - purchased F13 M6 couple months ago, great car, mildly tuned but not engine itself, just intake really. Runs great in general and being new to this engine/car I didn't notice anything terrible on the test drive. One thing I have done since ownership is do a cold start delete which has served to highlight this issue more, but I'm 99% sure the issue was there all along.

So, the issue - On cold starts, i.e. when starting after sitting overnight, id seems to start and rev correctly. Then after about 20 seconds, it starts idling roughly, the revs drop and then it recovers by surging and then this repeats a number of times, for about 30-45 seconds. Here is a clip I recorded the other day, sometimes it's worse, but this gives a good idea. Please watch with sound too

https://www.youtube.com/watch?v=UXlJaj0tL6k

When the revs drop you feel it in the car. When trying to drive during this time it kangaroos like crazy, I have to wait for it to settle.

Until recently I thought it was only during startup but now I think that when I come to a stop at any time, the idle is not as smooth as it should be, the needle does move slightly and what's even weirder is that when creeping along before stopping, as soon as I brake the revs go up over 1k quickly then quickly drop back down. All a bit strange. (that part could be normal though).

All I have done so far mechanically is a MAF sensor change.

In terms of mapping, I have been running Bootmod3 however I am currently back on the stock tune and it's still doing it. With the cold start function ON, although the revs are higher, they are still not stable like I would expect, though its less noticeable than with cold start off I admit.

Oh an no error codes are thrown at all.

Basically looking for advice on next steps. I have ISTA, should I be looking at doing any specific diagnostics tests?

My next action is to replace plugs and coils because I just like to know they are refreshed, but I'm not just assuming that will fix my problem.

Any advice would be great as it's one of 2 issues that are ruining the enjoyment a little (I'll post the other one separately!)

Thanks for reading

(PS. I cross posted from the UK forums but I guess I might get more help here...)

[M5Rick]

Originally Posted by 325_bucks

Sorry for the long post, appreciate anyone reading to give me advice...

Hi all

Imposter here from the M6 side, but that side is quite quiet so I hope you don't mind me asking here as it's going to be relevant to both.

As short as I can - purchased F13 M6 couple months ago, great car, mildly tuned but not engine itself, just intake really. Runs great in general and being new to this engine/car I didn't notice anything terrible on the test drive. One thing I have done since ownership is do a cold start delete which has served to highlight this issue more, but I'm 99% sure the issue was there all along.

So, the issue - On cold starts, i.e. when starting after sitting overnight, id seems to start and rev correctly. Then after about 20 seconds, it starts idling roughly, the revs drop and then it recovers by surging and then this repeats a number of times, for about 30-45 seconds. Here is a clip I recorded the other day, sometimes it's worse, but this gives a good idea. Please watch with sound too

https://www.youtube.com/watch?v=UXlJaj0tL6k

When the revs drop you feel it in the car. When trying to drive during this time it kangaroos like crazy, I have to wait for it to settle.

Until recently I thought it was only during startup but now I think that when I come to a stop at any time, the idle is not as smooth as it should be, the needle does move slightly and what's even weirder is that when creeping along before stopping, as soon as I brake the revs go up over 1k quickly then quickly drop back down. All a bit strange. (that part could be normal though).

All I have done so far mechanically is a MAF sensor change.

In terms of mapping, I have been running Bootmod3 however I am currently back on the stock tune and it's still doing it. With the cold start function ON, although the revs are higher, they are still not stable like I would expect, though its less noticeable than with cold start off I admit.

Oh an no error codes are thrown at all.

Basically looking for advice on next steps. I have ISTA, should I be looking at doing any specific diagnostics tests?

My next action is to replace plugs and coils because I just like to know they are refreshed, but I'm not just assuming that will fix my problem.

Any advice would be great as it's one of 2 issues that are ruining the enjoyment a little (I'll post the other one separately!)

Thanks for reading

(PS. I cross posted from the UK forums but I guess I might get more help here...)

Rather than shooting in the dark and replacing things I would suggest going back to the standard air filter set up and see how it behaves with those and restore the cold start factory setting.

[325_bucks]

Originally Posted by M5theonlyone

Rather than shooting in the dark and replacing things I would suggest going back to the standard air filter set up and see how it behaves with those and restore the cold start factory setting.

Sorry if I wasn't clear. I have tested the car with the standard stock map, with cold start OEM, basically flashing it back to normal. As I said although the cold start masks the problem a little, it's still there.

Secondly I don't have the original intakes, only the Eventuri ones that are on there currently

[M5Rick]

Originally Posted by 325_bucks

Sorry if I wasn't clear. I have tested the car with the standard stock map, with cold start OEM, basically flashing it back to normal. As I said although the cold start masks the problem a little, it's still there.

Secondly I don't have the original intakes, only the Eventuri ones that are on there currently

In that case then if the plugs have never been changed then that would be a logical step. Mine is just about on 38k now with the original plugs and I have the new plugs ready to do at 40k,I also add redex at every fuel fill so why not start trying that.

[325_bucks]

Originally Posted by M5theonlyone

In that case then if the plugs have never been changed then that would be a logical step. Mine is just about on 38k now with the original plugs and I have the new plugs ready to do at 40k,I also add redex at every fuel fill so why not start trying that.

Redex injector cleaner?

The mileage is 41k, I don't know for certain if plugs have never been changed but on the assumption no, I think I will get them and do the coils too while I'm at it.

I'm going for the Bosch 8165 which I think are the latest recommended replacements, probably gapped a little smaller than stock.

[M5Rick]

Originally Posted by 325_bucks

Redex injector cleaner?

The mileage is 41k, I don't know for certain if plugs have never been changed but on the assumption no, I think I will get them and do the coils too while I'm at it.

I'm going for the Bosch 8165 which I think are the latest recommended replacements, probably gapped a little smaller than stock.

I use redex additive and the car has never missed a beat, it keeps plugs clean, primes the injectors and lowers Co2.

[325_bucks]

I changed my plugs and coils today, no difference to the issue at all.

I also performs a couple of ISTA tests like injector leak test and all clear.

Really stuck on next steps. As I said, it’s fine to start, then starts misfiring or whatever it’s doing, then smooths out again. It’s the fact that it does that specific pattern that is really confusing.

Anyone got any other ideas? O2 sensors? It has to be something that would only cause it to do it during 30-90 seconds after cold start only. Whether it’s leading to other problems I don’t know but I do feel idle when driving around is not as smooth or steady as it should be.

[M5Rick]

Originally Posted by 325_bucks

I changed my plugs and coils today, no difference to the issue at all.

I also performs a couple of ISTA tests like injector leak test and all clear.

Really stuck on next steps. As I said, it’s fine to start, then starts misfiring or whatever it’s doing, then smooths out again. It’s the fact that it does that specific pattern that is really confusing.

Anyone got any other ideas? O2 sensors? It has to be something that would only cause it to do it during 30-90 seconds after cold start only. Whether it’s leading to other problems I don’t know but I do feel idle when driving around is not as smooth or steady as it should be.

02 sensors would be the next suspects in line as you completed plugs/coils change. I know you said the MAF's,both of them were replaced with new before you bought the car but just to satisfy take them out and clean them to be sure.

[325_bucks]

Originally Posted by M5theonlyone

02 sensors would be the next suspects in line as you completed plugs/coils change. I know you said the MAF's,both of them were replaced with new before you bought the car but just to satisfy take them out and clean them to be sure.

No sorry I changed the MAFs myself, only a week or two ago.

Should I change the post cat sensors too do you think?

Where do the pre cats sensors plug in?

[m5rosco]

I recently had a misfire at idle issue. Changed plugs and coils etc, no difference. No fault codes, smooth running tests came back as good etc. Diagnostics kept saying misfire on no 7. swapped injectors 7 and 8, still missing on 7. Compression test and leak down tests confirmed all was healthy. Further digging with fancy oscilloscope stuff found injector no 5 to be weak, yet nothing ever pointed to that. New injector fitted and coded and all is good again. Cant thank A Reeve Performance in Kings Lynn UK enough. Really knows his stuff. For peace of my own mind I will be changing all the injectors now.

https://www.facebook.com/areeveperfo...69905676398081

[325_bucks]

Originally Posted by m5rosco

I recently had a misfire at idle issue. Changed plugs and coils etc, no difference. No fault codes, smooth running tests came back as good etc. Diagnostics kept saying misfire on no 7. swapped injectors 7 and 8, still missing on 7. Compression test and leak down tests confirmed all was healthy. Further digging with fancy oscilloscope stuff found injector no 5 to be weak, yet nothing ever pointed to that. New injector fitted and coded and all is good again. Cant thank A Reeve Performance in Kings Lynn UK enough. Really knows his stuff. For peace of my own mind I will be changing all the injectors now.

https://www.facebook.com/areeveperfo...69905676398081

Was your misfire there on every idle? Mine is only there for the first cold idle of the day, and comes on after 30 seconds and goes away after 90 seconds, then it’s not there again until the next day

[Spacecpe]

Rough cold starts are almost always related to injectors as they can leak a bit overnight and when you go to start the extra fuel doesn't burn right away. As soon as it burns, the car is back to normal. I would look at those injectors closely. You don't wanna be messing around too much, if one of them is leaking, it can break down the oil and cause cylinder scoring and other bigger issues.

[325_bucks]

Originally Posted by E90 M335i

Rough cold starts are almost always related to injectors as they can leak a bit overnight and when you go to start the extra fuel doesn't burn right away. As soon as it burns, the car is back to normal. I would look at those injectors closely. You don't wanna be messing around too much, if one of them is leaking, it can break down the oil and cause cylinder scoring and other bigger issues.

Even if the rough running doesn’t start until 30 seconds after starting? And I’ve done an injector leak test with ISTA which was clear

[Spacecpe]

I didn't see that 30s part, my bad. If so, to me it point at O2 sensor. On cold start O2 are completely disregarded and are on open loop until they heat up (usually about 30s).

[325_bucks]

Originally Posted by E90 M335i

I didn't see that 30s part, my bad. If so, to me it point at O2 sensor. On cold start O2 are completely disregarded and are on open loop until they heat up (usually about 30s).

That’s encouraging based on symptoms and explains why it doesn’t start until 30 seconds after start but would that also explain why it stops after a further minute or so (and then leave an idle that’s smooth although I think may not be as smooth as it should be)

[Spacecpe]

Most likely a slow warming O2 sensor.. once its warm (past the 1min) it gives the DME the right data to run smooth.
Its a good starting point.. usually with misfires, you wanna go plugs and coils first, O2 after (depending on symptoms) and injectors last.

[325_bucks]

cool, well I got sensors coming tomorrow so will swap them out (only the pre cat ones for now) and see what happens. Interestingly I just disconnected the sensors and started the car to see what happened. It was exactly the same, nothing better OR worse

[Rjrzwhips]

I own a 2013 M5 and a 2012 X5. I recently experienced the same problem with my X5. I noticed a low battery warning message the same time. I charged the battery and the idle problem went away. I did not drive the car for a few days and the idle surge came back. I checked the battery and it was low again. Again I charged it and the idle was normal. Planning to replace the battery. These cars have so much electronics that low voltage can cause problems

[rockyfeller]

Great insight E90. Haven't heard those explanations and it makes sense.

[325_bucks]

changed o2 sensors today (pre cat), unfortunately, no difference to the problem at all.

Same as per the video above, starts smooth with a tiny amount of fluctuation, then starts dropping and overcompensating to high and this cycles for about another minute and then it settles again.

Really stumped now. Could a low voltage battery really do this the way I've described? would it not do it from the moment it's started?

Am I looking at injectors next then?

[M5Rick]

Originally Posted by 325_bucks

changed o2 sensors today (pre cat), unfortunately, no difference to the problem at all.

Same as per the video above, starts smooth with a tiny amount of fluctuation, then starts dropping and overcompensating to high and this cycles for about another minute and then it settles again.

Really stumped now. Could a low voltage battery really do this the way I've described? would it not do it from the moment it's started?

Am I looking at injectors next then?

I don't think it's injectors.Once an injector plays up it keeps playing up. I had the fuel filter changed at 25k at BMW before I purchased it,as far as I know on UK cars it's a cartridge underneath the floor pan and I have my BMW book ticked and stamped that it's been done, so it might be worth doing that unless its been done already..and put that red redex in the tank,it's good stuff.
On US cars the open fuel filter is the fuel tank.

[325_bucks]

yes its a UK car and fuel filter was on my list. I'll double check the history and see.

I have the redex stuff ready to go so will add that later when I get fuel and see what happens but I think by the consistency of the issue, it seems to be an actual fueling or ignition issue of some sort.