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Discussion Starter · #1 ·
Hi. I just got an e46 m3 and its been driving fine. One day at idle it started to misfire and shake the whole car. I get zero codes. When the car is on coldstart its no misfire but the second its done with coldstart the misfire startes hard at cylinder 1 and 6. i have new sparkplugs and coils and i have done a compression test and its all good. Any tips?
 

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If you had M54 I would say that you have a failing IAC and/or DISA. But since you have S54 I’m not super good with their architecture when it comes to the intake. S54 doesn’t use DISA. It’s should be that area after the intake but I’m not certain what regulator it uses down there. Anybody can pin point better?
 

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Hi. I just got an e46 m3 and its been driving fine. One day at idle it started to misfire and shake the whole car. I get zero codes. When the car is on coldstart its no misfire but the second its done with coldstart the misfire startes hard at cylinder 1 and 6. i have new sparkplugs and coils and i have done a compression test and its all good. Any tips?
Classic. Move #1 coil and plug to #2. See if misfire moves. Possible bad new coil or spark plug.
 

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When the car is on coldstart its no misfire but the second its done with coldstart the misfire startes hard at cylinder 1 and 6
How do you define when it's cold start and when it finished coldstart? To me, cod start when the O2 sensors are opened loop, and after when the DME use the O2 sensors to close the loop, but how can you tell without looking at the data?

I guess after coldstart the DME closed the loop with O2 sensors and the system was running too lean and causing misfire. You need use OBD2 and run a data log then post the CVS file for troubleshooting.
 

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Discussion Starter · #7 ·
How do you define when it's cold start and when it finished coldstart? To me, cod start when the O2 sensors are opened loop, and after when the DME use the O2 sensors to close the loop, but how can you tell without looking at the data?

I guess after coldstart the DME closed the loop with O2 sensors and the system was running too lean and causing misfire. You need use OBD2 and run a data log then post the CVS file for troubleshooting.
thats the thing. i dont have any codes
 

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Discussion Starter · #9 ·
You used codes reader or just based on Service Engine soon light?
Use an OBD2 reader and log the data.
when starting the cold engine, the O2 sensors will be in closed loop after about 60 sec. So exactly when the misfire happened, much later than a few minutes?
When i try to use obd2 i just get a feil to connect to ecu error
 

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Discussion Starter · #12 ·
Hi. I just got an e46 m3 and its been driving fine. One day at idle it started to misfire and shake the whole car. I get zero codes. When the car is on coldstart its no misfire but the second its done with coldstart the misfire startes hard at cylinder 1 and 6. i have new sparkplugs and coils and i have done a compression test and its all good. Any tips?
Found the problem. Cleaned the vanos and the car runs as it should
 

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I don't think so. How can a bad ICV (you wrote IAC) or bad DISA doesn't show the rough idle during cold start but only after cold start as OP reported?
1) It's full proper name is Idle Air Control Valve. Potato-Potahto.
2) I had rough idle after SAP was done with suction around 15-30 second after cold start. Not a mystery to me.
 

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Misfire starts as soon as the car stops being loudly and that is what ppl have told me when the cold start is done
The loud noise could be the SAP running. Does your car have the secondary air pump (near the coolant reservoir)? If yes then it should be done around after 60sec.
When i try to use obd2 i just get a feil to connect to ecu error
Have you tried INPA or VEEPEAK ODB2 reader with OBD Fusion app?
 

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I got obd2 to read 00004D code
You should look this up and list the description here so we don't have to do this.
4DDME: Signal, intake-air temperature sensor
Use INPA or your reader to display the intake temp and it should be 10 or 20C higher than ambient but should not be anything so crazy. This could be the problem if the sensor was bad or signal was bad, causing DME calculated bad mixture.
 
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