Cold Start Issue - '03 2.5i Z4

[kalali]

Hello chaps. My Z4 had been totally trouble free for 94K miles up until two weeks ago when it stalled during warm up on a cold day. It starts right back up and runs and stalls again. This could happen a couple of times and then it runs perfectly once warmed up. No codes whatsoever. I have been told this could be a vanos issue but there is no rattle or loss of power, just stalling during cold starts. I disconnected the vanos intake solenoid and secondary air pump separately but the symptoms did not change.
Has anyone else had this problem? I also measured the voltage into the vanos solenoids and they both read right around 8 volts. Shouldn't they be at battery voltage, 12+ volts? Battery is brand new and I'm running out of ideas. The absence of code is mystifying as well. I'd like to rule out simple stuff before resorting to the vanos repair, especially since the car runs just like new when it overcomes the cold start issue. Thanks in advance and happy new year.

 

[Adamski]

Hmm strange one. Have you tried changing plugs, filters etc? Failing that coil pack issues have not been unheard of...


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[kalali]

I checked the plugs a little while back and looked fine. Filters are good as well. Shouldn't be coil since the car runs perfect as soon as it is warmed up and never stalls during warm start ups. It must be something related to temperature. Based on what I've read the symptoms do match a bad vanos on some cars but it is still very rare. Most have rattling and loss of low end power. I have neither. I'm still scratching my head why I'm only getting 8 volts into the solenoids. I thought all connectors are supposed to put out battery voltage...

 

[dyshipfakta]

How is fuel trim calculated for cold starts on the z4. My mgf had similar issues wen coolant temperature sensor was faulty. This caused the mixture to be incorrect at cold start but fine when it had warmed up etc. Would be worth tryin an obd2 scanner this is the kind of fault that would generate a code.

 

[Whitehouse]

i had a similar issue a few weeks ago! it would start for about 10-15 seconds then die, it did this for quite a few cold days then it did it one day and the eml came on and wouldnt start again, took it to my local bmw specialist and apparently he updated the software and reset the throttle bodies? whatever he did though it fixed it

 

[kalali]

Thanks every one for the feedback. Part of the issue is I get no codes. All sort of seemingly unrelated warning lights including engine and DTC come on right before the engine stalls but nothing is registered. Makes it really hard to isolate. Once warmed up the car drives like new...

 

[Whitehouse]

Thats what was happening with mine, usually traction control light and something else would flash up, i just left it and put it down to cold weather until one day it did actually throw a code up! There wasnt an issue with mine when warmed up aswell, it was always cold starts. Yours might end up being fine but just be warned mine eventually threw a code up didnt want to start until it had warmed up outside and after 7-8 times trying to turn it over. Typically it was the first day of my new job aswell! Great start! :roll: