Any Ideas..?

[wills]

Hoping you can help with this;

- Over past few months car has felt mildly hesitant sometimes
- yesterday it made a major misfire, ie car jerked & then it was fine
- tonight, when i blipped the throttle there is a brief 'rush if air' noise and then the revs rise (delayed). Performance affected.
- restart engine & all is fine again ie no air noise & engine smooth

No fault codes etc. A recent dyno showed the MAF may be playing up but again no fault codes

Thoughts anyone..?

 

[Ewazix]

Most irritating of faults! There are lots of other possibles including fuel delivery but a few likely culprits for starters are,

Make sure the battery is good and fully charged.
Check the security of all power/ignition leads/wires
Check for air leaks around the air intake, listen under the bonnet with someone blipping the throttle. If you have non-standard air intakes return to standard spec.
Most likely a faulty camshaft position sensor - common BMW problem but not too expensive or difficult to replace. Can be hard to diagnose if you don't get a fault code but should be picked up on an extended diagnostic.
Ignition coil pack breaking down - can normally be picked up on a diagnostic or sequentially exchange with a known good item one at a time.
Spark plug breaking down, visual inspection may reveal one dirty/burnt or with damaged exterior insulations, sequentially exchange with a known good item one at a time or check on a diagnostic.
Dirty MAF sensors can cause problems, should be picked up with diagnostic or try cleaning it with proprietary spray, http://www.realoem.com/bmw/showparts.do?model=BT52&mospid=47797&btnr=13_0995&hg=13&fg=15
O2 Sensors seem to be a common problem on many makes, I've not dealt with one but they can be tested with a meter or should be revealed with a diagnostic.
There are a shed load of other sensors including 'knock' or pre-ignition detection which can also cause this.
*hit in the fuel (a possible cause, not a cure)

Whatever you do make sure you test after each item is checked/replaced or you will drive yourself mad wondering which one cured it. But the short answer with type of problem is probably to get it run on a diagnostic computer. Good luck.

 

[wills]

A very useful response, many thanks.

To add to the issue, it seems once the ignition is turned off & on, it drives fine & flies like a rocket. The difference is Lada versus Ferrari..

I might just dump it with BMW dealer for a while, but will print off your post as a checklist.

Thanks again!

Ps - what's strange is before i reset the ignition, i blipped the pedal at idle, get a brief vacuum / induction noise & delayed throttle response. After reset, back to normal ie instant throttle & no vacuum noise - odd..

 

[Ewazix]

Ps - what's strange is before i reset the ignition, i blipped the pedal at idle, get a brief vacuum / induction noise & delayed throttle response. After reset, back to normal ie instant throttle & no vacuum noise - odd..

........in which case it could still be any of the above but would add air induction valves to the possibles list, I'm not sure if your engine has the Valvetronic system (a clever replacement of the conventional butterfly flap) or a later unit, but a sticking air valve or lagging in induction intake air would give these symptoms. Best get it on the machine! I'd be interested in the result,