MAF diagnosis - what else to look at.

[johnfm]

2007 2l naturally aspirated petrol.
Not been happy with low rev running lately. Under 2k it is sometimes smooth, but quite a lot of hesitation.

No engine lights coming on, so I assume coils packs and injectors are ok.

Disconnected the MAF and drove about 7 miles to the shops with NO noticeable difference.

But when I restarted after shopping it threw an engine light and went into limp mode. Reconnected and engine light cleared. Back to its hesitant self.

So, does the first journey with MAF disconnected suggest the MAF isn't doing its job.

[robsco]

Doesn't sound like MAF to me. Firstly, you'd expect the engine light to come on as par for the course. Secondly, you'd expect with the MAF disconnected that the hesitation would disappear to a great extent - when the MAF is disconnected, the ECU reverts to a default air flow setting, you should have been able to tell the difference. Perhaps someone will come along and correct me, but I'd be looking elsewhere.

[Leeds220]

Yep, pretty certain it isn't the MAF. When it went on my Golf, as soon as you disconnected the sensor it drove pretty much like normal.

Sorry can't help with what else it could be.

[Y282]

Fuel filter?

[EssThree]

Hi newbie here...

Fuel filter maybe? I've recently had MAF related issues on my car. I was getting hesitation etc as you described. I changed the MAF which made some difference but the most noticable difference was changing the fuel filter, car is now so much smoother.

[EssThree]

Y282 said:

Fuel filter?

Damn, must type faster!

[Y282]

EssThree said:

Y282 said:

Fuel filter?

Damn, must type faster!

Its often simple stuff like this that slips through a diagnosis.

[johnfm]

Ok.
Car is a 34k mile, 2007 320i.

I'll give the fuel filter a try - as I expect it is cheap.

Re: the MAF and disconnecting it - it is not running so bad as to be undriveable (unlike hte time my Audi did a MAF and it wouldn't do more than 2000 rpm)

So I guess that leaves fuel filter, injectors or coils.

[Yiliterate]

Had some hesitancy with my BMW recently (though was more noticeable at higher revs), which was traced back to a faulty temperature sensor making the engine run lean...

[EssThree]

Y282 said:

Its often simple stuff like this that slips through a diagnosis.

Yes, might be worth it for the OP for the sake of ~£10

[johnfm]

Yiliterate said:

Had some hesitancy with my BMW recently (though was more noticeable at higher revs), which was traced back to a faulty temperature sensor making the engine run lean...

This is interesting.

What temp is it sensing?

The ran noticeably crap the thee hot days we had last week.

[Leeds220]

Just remembered - another time I had a similar problem the throttle bodies needing cleaning. The garage said it was the result of cheap supermarket petrol, lots of short trips or a combination of both. Might be worth a look as it could be a cheap fix and cleaning them up isn't going to hurt anyway.

[rhinochopig]

Coil packs don't always show a warning light.

[rhinochopig]

Coil packs don't always show a warning light.

[Yiliterate]

johnfm said:

Yiliterate said:

Had some hesitancy with my BMW recently (though was more noticeable at higher revs), which was traced back to a faulty temperature sensor making the engine run lean...

This is interesting.

What temp is it sensing?

The ran noticeably crap the thee hot days we had last week.

I think it was the coolant temperature sensor on the thermostat housing. I would caveat though that replacing it cured the problem for a while, but I took the car out for a good run last weekend (c.30 miles) and a couple of miles from home the issue started to re-occur, so will need some more investigation...

[dan5oclocksmith]

If it was a coilpack you'd have an intermittent misfire.

Have you had it read for fault codes? That might give an indication, even if the engine light isn't on.

Otherwise, you need to check for leaks in the induction pipes, and whip the plugs out and check them and the coilpacks visually.

[johnfm]

Hesitation is only under 2000 rpm. Does the 320i have vanos? Could it be related to that?

If I get a creader v does anyone know I the real time display will tell me much?

[Dab of oppo]

For the sake of £40 I'd stop guessing, take it to an independant BMW specialist and have them run a diagnostic on it.
There may be no engine light on but it may have something stored that may point to an underlying problem.

[Y282]

Its a bmw?

Definitely do fuel filter, then check all your air hoses are connected and that your intake elbow is fitted tightly and has no cracks in the ribbing.

[johnfm]

Dab of oppo said:

For the sake of £40 I'd stop guessing, take it to an independant BMW specialist and have them run a diagnostic on it.
There may be no engine light on but it may have something stored that may point to an underlying problem.

I already have - they were a bit pointless, as there were multiple, spurious stored codes for too many different sensors for them to make any sense.

Sadly, when computer says 10 things, some (not all) garages just start replacing things whether or not they can prove they are faulty.