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Discussion Starter #1
Hi all -

My 2011 328i has about 100k miles. About a week ago it started to misfire while at idle. Just a light, brief shake. No misfires while driving. No service engine light nor error codes.

I had had a similar issue about a year ago, with an error code indicating a cylinder 2 misfire. I replaced all spark plugs, and the ignition coil for cylinder 2 only. The issue was resolved.

In light of that I decided to try replacing the remaining ignition coils today. Well following that the car shakes violently and then stalls out. Service engine light is on and I***8217;m receiving the following codes:

P0305 p
P0303 p
0304 p

I also tried cleaning the MAF, to no avail.

Any ideas here???

3/2007 328xi E91
2,938 Posts
NOT everything that causes a "shake" in the engine, particularly at idle, is a "misfire", and NOT all "misfires" are related to ignition: plugs, coils & associated wiring & connectors, according to the description in Bentley (p. (OBD-4) of how misfire is detected:
"Misfire detection. This strategy monitors crankshaft speed fluctuations and determines if an engine misfire occurs by monitoring variations in speed between each crankshaft sensor trigger point. This strategy is so finely tuned that it can determine the severity of the misfire."​

So a "Misfire" as computed by the DME based upon Crankshaft Sensor "speed signals" is a slight decrease in RPM for ~ a millisecond, which is evidence that the particular cylinder whose power stroke just occurred (as computed by the DME) did NOT produce as much power as the cylinders immediately BEFORE & AFTER that cylinder in the firing order. ANYTHING that can cause that power loss, including injector function or any electrical fault in coil or injector circuit, can cause a "Misfire" by that definition.

There are things that can cause idle speed fluctuations or shaking which do NOT meet the DME algorithms' definition of "Misfire", in that ALL cylinders have reduced power for an instant. The example of that which seems to be reported most often on this forum is a vacuum leak, or air entering the intake manifold which did NOT pass through the MAF Sensor area and is therefor "unmetered." Since the EFI is essentially adding the right amount of fuel for the amount of air that the MAF is telling the DME the engine is drawing in, such a "vacuum leak" results in too LEAN fueling, and a ragged idle.

So check for cracks in the hose that comes from the Valve cover to the Intake Manifold, and any other possible sources of air leak. Starting Fluid or spray ether can also be used on a COLD engine soon after startup to see if idle speed increases when a particular area under the intake manifold, or toward the rear of the engine is sprayed. This spray is momentarily achieving proper fuel/air mixture of an otherwise too lean mix if the idle speed increases. So the likelihood, based upon the information provided to date, is that you did NOT have a misfire situation BEFORE you changed the coils, but PROBABLY had a ragged idle due to LEAN fueling or other issue that affected ALL 6 cylinders equally.

As for why you now have misfire codes that you did NOT have BEFORE changing the coils, there are a number of possibilities, depending upon what was done, and we need more details to even make a SWAG.


1) What brand and part# were the coils you just REMOVED, & what was the brand & part# of the coil installed a year ago which I understand you left in place?

2) What is the brand & part# of the 5 coils you just INSTALLED?

3) Did you used any kind of lubricant, such as dielectric grease, on the plug boots of the new coils, and if so, WHAT?

4) Did you pay close attention to the proper seating of the coils ON the plugs & INTO the plug wells?

5) Did you carefully inspect the coil Connectors to make sure pin sockets were NOT displaced, and that the Connectors locked positively and easily?

6) Did you inspect the Brown Ground wires and their groundpoint studs & nuts, to make sure the nut was secure on each? (You should NOT have loosened or removed either nut to change the coils).

If all else fails, simply try to return to the previous status quo by reinstalling the coils you removed. If different brand (e.g. Bosch vs. Delphi) that ALONE MAY explain the issue.

Please let us know what you find,
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