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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 08-31-2015, 06:33 AM   #1
Registered User
Join Date: Aug 2015
Location: LanCo, PA
Posts: 18
My Ride: 2001 325i
Poor idle, miss on cyls 1, 2, and 3 when left idling.

New to me '01 325i. Car runs fine if I start it up and drive. It's only when I'm in traffic or let it idle for a minute or two before taking off I get a misfire on 1, 2, and 3. I am planning on swapping to the M56 aluminum valve cover once I figure out for sure which coils to use but is there anything else I should check out for this issue? The weird thing is if it starts missing I can get up to speed, disengage the clutch, turn the ignition off, wait a few seconds, the turn the ignition back on and engage the clutch and the miss will be gone. If I drive long enough with it missing it usually goes away after 10 minutes or so.

I've never experienced such a strange miss but this is my first BMW.
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Old 08-31-2015, 06:59 AM   #2
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Join Date: Nov 2009
Location: Fairfax, VA USA
Posts: 19,549
My Ride: 330CiC, M5, X5
Not sure I would focus on the M56 valve cover at this point, not sure how well this may work out for a number of reasons.

As for the Misfire, what is happening is Misfire with Fuel Cut Off, this is why shutting the engine off and restarting it clears the problem.

You have a vacuum leak, a really problem O2 sensor (unlikely) or a weak fuel pump.

Need OBDII data and Freeze Frame info to get a better idea as to what is happening.

Lower intake boot, CCV and hoses, DISA or power brake booster are the most likely vacuum leak areas.

Read this -

Get an OBDII smart phone/tablet App and interface, typically $30 or less. These Apps are usually best for drivability issues and they support Emission Readiness Monitor Status, Freeze Frame and Live/Realtime data. They are also great for Logging data for review after the car has been driven and can really help find unusual problems.

Android - Touch Scan for $5.00 and ELM327 OBDII to Bluetooth interface.

iProduct - OBD Fusion for $9.99 and ELM327 OBDII to Wifi interface.

Some people prefer to have an extension cable to keep the interface away from their feet.

Something like these cables are often of interested:



I usually suggest getting the OBDII interfaces from Amazon if you are located in the US/North America. Make sure you choose an interface that indicates that the order will be "Fulfilled by Amazon" otherwise you may be waiting for WEEKS for an interface to arrive from Asia. Ebay is another option, but pay attention where the interface will be shipped from, again weeks for an interface from Asia, so if you can wait and want to try to save some money, go for it, but if you need an interface soon, choose wisely.

Read the 2 links below:



Need to see Freeze Frame info if the SES/CEL/MIL is on and Fuel Trim values at both warm idle and a steady highway cruise between 45-60 MPH.

MAF issues, first cleaning a MAF RARELY resolves anything, the only thing it usually cleans is your wallet.

If you have recently replaced the MAF, put the original back on the engine until you sort out all of the obvious issues. There are MANY counterfeit MAF's on the market and the major trap is ASSUMING the MAF is not the problem since it was recently replaced. Also quite often the MAF is NOT the cause of idle related Lean conditions and misfires, faulty MAF's usually under report the airflow as a percentage and are more of a problem at highway cruise speeds and not engine idle.

Unplugging the MAF will often cause the engine idle to be smoother, reduce or eliminate idle misfires. This DOES not mean the MAF is bad, it is due to the DME going into a fixed fuel Map mode that is typically by default Richer than when the MAF is connected and this will mask Lean conditions caused by intake and/or crankcase air leaks.

P0102 means for some reason there is not likely a signal from the MAF. Verify if the MAF connector is properly plugged in, sometimes the female terminals in the connector are spread and loose on the MAF pins, sometimes there are broken wires inside the wiring harness between the MAF and the wiring box near the throttle body and sometimes the MAF just is bad with no output signal.

WARNING - DO NOT buy a cheap ebay MAF, there are many Asian counterfeits on the market that do not work properly. See of there is an MAF reading in Grams/Sec. Most E46 have an idle MAF reading of between 3.5-4

Note, there may or may not be Lean Codes showing up. Lean Codes usually trigger at around 10% Fuel Trim values or higher. Keep in mind that sometimes these engines can have a Lean condition that does not or only intermittently triggers Lean Codes. This is why monitoring the Fuel Trims in real time is important. Ideal Fuel Trim values are typically in the 0% to +2.5/+3.0% range.

Read this thread - http://forum.e46fanatics.com/showthread.php?t=1057387

Make ABSOLUTELY sure the O2 sensor wiring has not been mixed up, read these links:



Read my "BMW 20 Questions" comments in this thread - http://forum.e46fanatics.com/showthread.php?t=1059972

Check for or be aware of cracked valve covers and bad valve cover gaskets:




This information ASSUMES that spark plugs have been checked/replaced. If they have not been inspected, you also need to check for oil filled spark plug wells due to a leaking/cracked valve cover gasket.


Search YouTube for Scotty Smoke Test. Do what Scotty does or build a tester from related video. Remove the oil fill cap and make sure the crankcase fills up with smoke, put the oil fill cap back on and check for leaks around the valve cover, oil fill cap, dipstick tube and CCV hoses. Cracked valve covers are pretty common on the E46 as it ages.

Note that the Scotty Smoke Test method is not so good for smaller air/vacuum leaks or fully filling the engine crankcase, for this you really need a smoke machine that can provide a solid and continuous low pressure smoke stream. So plan on building a smoke tester of you thing you will use if more than once or may have smaller and harder to find leaks.
Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 08-31-2015, 07:00 AM   #3
Registered User
Join Date: Jul 2008
Location: USA
Posts: 4,949
My Ride: 2001 330Ci
Is the fuel pump original? If it is it's time for a new fuel pump and a fuel filter. Also, replace the 3 short (less than 2" long) rubber fuel hoses at the filter. And, replace the 6 clamps. Hey, your car is 15 years old. It's been though a lot in those years!
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Old 05-20-2016, 08:10 PM   #4
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Join Date: Aug 2015
Location: LanCo, PA
Posts: 18
My Ride: 2001 325i
Figured I'd update this thread. Problem mysteriously went away after the car sat for a month waiting on parts for a... clutch job. Don't know why or how, but it was gone. Not shortly after that I had the parts to swap the M56 VC and did so eliminating the external CCV but the problem had already vanished on it's own.

There was a pretty decent crack in the plastic VC that I did see once it was removed, though. Curious why it didn't give me any additional trouble for the few months I drove it after the clutch job.
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