Intermittent Rough Running/misfire - No fault codes

[Ianb]

My car has been suffering from intermittent Rough running/misfire, makes no difference if it's hot or cold, it just comes and goes, not sure how to describe it apart from it feels flat when driving at normal 2-3K revs and the vibration can be felt and heard even when letting off the throttle and slowing down.

The only fault code I have is a shadow/pending P0128 which seems to point towards the thermostat, or if not the coolant temperature sensor.

Can plugs/coils cause this?

[sapote]

It's hard to say due to no codes (P0128 means coolant was too low temp could be thermostat always opened but this shouldn't cause the rough running). Remove all plugs and show good pics of the tips.

[Darbshaw]

I had this issue on my car, it wasn’t until I replaced plugs and coils, did my vanos, fuel pump etc. Eventually I finally took the time to do a compression test and found I had a blown head gasket. I know mine is a worst case scenario but I had enough with trying to chase down all the codes and that pesky misfire that kept coming back. I did also have a engine coolant temp implausible code but I don’t know if this was relatable to the issue


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[eacmen]

I had this issue on my car, it wasn’t until I replaced plugs and coils, did my vanos, fuel pump etc. Eventually I finally took the time to do a compression test and found I had a blown head gasket. I know mine is a worst case scenario but I had enough with trying to chase down all the codes and that pesky misfire that kept coming back. I did also have a engine coolant temp implausible code but I don’t know if this was relatable to the issue


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I feel like every S54 has this coolant temp implausible code... never affected either of our cars.

Could be an early sign of a plug or coil going bad. If you ever get it to happen at idle, pull over and disconnect the coil harness connector one at a time. If you disconnect a coil you should audibly hear a misfire on the cylinder you disconnected. If you disconnect a coil and the engine seems unaffected then its either the plug or the coil.

[Ianb]

Thanks for replies.

Darbshaw - that makes me feel really good fingers crossed it's not head gasket. Can you describe what your misfire was like? Aren't head gasket failures normally noticed under load, with a noise aswell?

I will check the plugs and coils, I know the coils are all originals.

Could a fairly MAF sensor give this sort of problem? Is it worth cleaning it?

Might also be worth mentioning that I have only noticed this problem after not using car for 3months because I had the backend apart for reinforcement/paint underside. When I removed the fuel tank I did tip it over to empty last if fuel out which made a "donk" noise which I assumed was the sender float, is there anything on the pump/fuel pickup that could have become blocked/twisted?

[eacmen]

Darbshaw - that makes me feel really good fingers crossed it's not head gasket.

I will check the plugs and coils, I know the coils are all originals.

Could a fairly MAF sensor give this sort of problem?

Debugging MAF is easy. Unplug it and see if it still happens. ECU will revert to AlphaN with MAF unplugged.

Also log fuel trims if you can, might indicate an issue. But usually codes are thrown in that case.

[enjoy_m3]

Before you spend any money, do a simple compression test.

[Arith2]

Before you spend any money, do a simple compression test.

He's gotta buy the compression kit though....

I agree it's a good thing to do just for the heck of it. Plugs and coils are usually the culprits if not a vacuum. We all get the coolant temp implausible code. It's a BMW, you can't ever fully satisfy it.

[Ianb]

When you say log fuel trims do you just mean check what they are or actual record them as you drive?

[Darbshaw]

I got my fingers crossed for you OP. I was left chasing a multiple cylinder misfire that was extremely intermittent. Causing a rough idle most the time and occasionally heavy misfires that rattled the whole car to death. I ended up replacing a lot of stuff before the ugly pinging sound from detonation came up.
I still feel that it’s personally good to get that compression done just so you can write that off as not being an issue. Avoiding mine caused a lot more damage and warranted a engine rebuild.


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[eacmen]

When you say log fuel trims do you just mean check what they are or actual record them as you drive?

Log them while you drive and especially when the misfires are happening.

While sitting in the garage long term will tell you some useful info , but short term changes while you drive.

[Ianb]

What program can I use to do that? Would that show if there was a fuel pump problem or not? Thanks

[eacmen]

What program can I use to do that? Would that show if there was a fuel pump problem or not? Thanks

I think most scan tools can do it since its an OBD thing. I use the schwaben/foxwell tool.

Or a k+dcan cable and BMWLogger should do it as well.

There are a bunch of yt videos on fuel trims but this guy generally does a good job of explaining things correctly:

https://youtu.be/oRX2V6_a3dc

[Ianb]

Thanks, I will give it a watch, I have k+d can cable so will look into bmwlogger.

[enjoy_m3]

He's gotta buy the compression kit though....

I agree it's a good thing to do just for the heck of it. Plugs and coils are usually the culprits if not a vacuum. We all get the coolant temp implausible code. It's a BMW, you can't ever fully satisfy it.

Your local pepboys, autozone, oreilly's rents them out for free with a deposit.