Chris_D said:
Ok thx for replying- i thought it was a longshot reviving an old thread, but what a coincidence ur having the same problem again!
Keep us posted re developments/fix etc please.
I'll be cancelling out a few things I think it might be with my motor- new (2nd hand) throttle body and crank/cam position on the way. Have cleaned TB and ICV but no change.
Could also be bad throttle posn sensor but that comes after trying replacement parts.
Sounds like we could have same problem so lets keep each other updated...
My thread here:
http://www.z4-forum.com/forum/viewtopic.php?f=3&t=90194
Bearing in mind this is a thread on the S54 M engine so might (probably) be different issues to what you have with the M54...
Having said that, INPA or DIS may help here rather than a generic code reader if you haven't already. That way you can see what values the various sensors are throwing out which might help pin point the problem.
TB issues are something I've not heard of on the S54, there's not really a whole lot to go wrong on it, the control for it on the other hand is a possibility. The actuator for example could go bad but again very rare I would suggest, more likely the TPS attached to it or the throttle bodies TPS are much more common. If one of these fail or gets sticky then in effect the DME wouldn't be able to accurately set the position of the butterfly's on the TB's which could well lead to these problems.
I can't advise too much on the M54 engine as I don't know it as well (at all really!), but on the S54 for sure I would be changing the 2 TPS sensors as the first port of call along with the MAF although that would be throwing a separate code if that had gone badly wrong. I would then move on to o2 sensors and then the thermostat which could also cause these issues if faulty. Then the TB actuator with the TB's (or single TB the M54 has I believe) themselves virtually at the bottom of the list. As said, INPA/DIS would help a lot here and probably give you a better indication.
Along with all that, I could also be a VANOS issue, dodgy solenoid etc. Always deal with what you've got fault code wise first. Cam/crank sensors will usually throw a code if they start playing up so again unlikely this is the issue, it would be pretty far down my list of things to change.
Just to throw another one in there regarding the coolant temp sensor/potential thermostat, I know on cold start up with the S54 DME it uses readings from that sensor and MAF to control idle until up to temp, if this sensor was faulty it would cause the issues you mention as well.
This is all my opinion based on the S54 though, I couldn't really suggest whether this is cross compatible with the M54.
EDIT srhutch beat me to it but yes in essence different engines, likely different causes!
