Why does my car run rough sometimes?

BUDFORCE · 31 Dec 2017 at 08:13

With the air sensor or mass air flow sensor, if it's playing up you'll likely need to replace it, not just clean it, it may be possible to diagnose it with software or maybe even go old school and try and get some readings off it using a meter, then look at a workshop manual to see the tolerances.

But tbh, I'd just replace the sensor.

titaniumx3 · 31 Dec 2017 at 14:07

Armageus said:
If you haven't already got one, it's worth picking up a Bluetooth OBD2 dongle, and a copy of Torque or similar for your phone.

With that you can monitor the various sensors, and may be able to spot the issue straight away (e.g. if there is no or intermittent reading on one)

Thanks, I will get one ordered.

Also, I've read something about the DISA valves on this car and some of the symptoms of these going bad, sound very similar to what I'm experiencing. Is this something to look into? Is there an easy way to test this on my car?

Lashout_UK · 31 Dec 2017 at 14:16

I would be inclined to take it to a knowledgeable BMW specialist, instead of ordering parts randomly and hoping they cure it. I know you've tried several garages, but it may be worth travelling to get one that actually knows what they're doing.

Scania · 31 Dec 2017 at 14:50

titaniumx3 said:
Hello again. Sorry for reviving this thread, but unfortunately I still have the problem. I took out the MAF sensor and cleaned it, but it made no difference, and it was pretty much spotless when I took it out anyway.

A MAF won’t look particularly dirty to the naked eye even if it is dirty enough to make a difference, they are very precise peices of kit and don’t need much crap on them to cause an issue.

Also, cleaning one can often do more harm than good, if you’ve used a cleaner that’s left any residue on the MAF sensors you’ll make matters worse.

As I say, to rule out the MAF you need to replace yours with a known good one, be it new or from a car that’s running correctly.

Differences in engine sound hints toward an air leak.

Ultimately, as said, you need to take it to a BMW specialist or even a BMW dealer and get them to diagnose the issue.

Swapping parts in the hope of finding the issue will prove a lot more expensive in the long run.

MatteH Oxford · 31 Dec 2017 at 22:43

Just a point to note regarding 'testing' the maf using an obd scanner - the reading for mass air flow will sometimes look like it is functioning (when it is actually broken) because you will see substituted values that are calculated from other functioning inputs such as tps and map sensors. The only way to confirm a faulty maf is from a test directly at the maf using a scope or suitable multimeter.

jpaul · 31 Dec 2017 at 23:04

Scania said:
if you’ve used a cleaner that’s left any residue on the MAF sensors you’ll make matters worse.

how did you clean it ? 'Valvoline EGR & Turbo Cleaner Valve Cleaner' - had spec'd this for a e46;
but susbequently found the air flow sensor rubber tube had a crack, which I resolved with some self amalgamating tape.

Scania · 1 Jan 2018 at 05:47

jpaul said:
how did you clean it ? 'Valvoline EGR & Turbo Cleaner Valve Cleaner' - had spec'd this for a e46;
but susbequently found the air flow sensor rubber tube had a crack, which I resolved with some self amalgamating tape.

I used something I got from the fitters at work - don’t know what it was but it was highly toxic! - they used it for the trucks, it didn’t do anything in my case as it turned out (after a new MAF was fitted) that I had a crack in the induction pipe.

Gaygle · 2 Jan 2018 at 12:56

Op, you got a video of this rough running and swirling noise?

DereksDontRun · 2 Jan 2018 at 13:17

dumb question, but it's not been remapped has it?

titaniumx3 · 2 Jan 2018 at 21:23

Gaygle said:
Op, you got a video of this rough running and swirling noise?

I'll get one uploaded when it happens next time and also do it when its running well. I've only got my phone to capture the sound, so I'm not sure it will pick it up, but I can definitely hear the difference with my ears. The main difference really is the feel of the car. When it runs well, revving the car out just feels very smooth (noticeably smoother than the 4 cylinder petrols I've driven in the past) and the engine makes a nice, clean and bassy 'humming' noise; sounds absolutely lovely and one of the reasons I bought the car in the first place. However when it is running 'rough' it feels and sounds a bit like a diesel, theirs a noticeble harshness and inconsistency to the engine sound; it's sounds asthmatic. While it is in this state, the whole car also just feels loose and rattly to drive, especially at low rpms/speed. The faster I drive the less noticeable the problem is. In fact, on the motorway it always feels smooth to drive.

The thing is, if it always sounded rough like this and I didn't know any better, I would just think that's how the car sounds and accept it for what it is, but given that it seems to operate in two different states, I feel like something is clearly not working properly. All the garages I've taken it to keep telling me that this is normal and that I should just pretty much accept it, which I doesn't sit right with me. I've not taken it to the main BMW dealer as they want to charge £135 just to inspect it, so I'm probably going to wait to till I have to service the car next and do it then.

DereksDontRun said:
dumb question, but it's not been remapped has it?

No, not that I am aware of. It's 2010 330i and had 35k on it when I bought the car. Everything is completely stock from what I can tell.

Scania said:
A MAF won’t look particularly dirty to the naked eye even if it is dirty enough to make a difference, they are very precise peices of kit and don’t need much crap on them to cause an issue.

Also, cleaning one can often do more harm than good, if you’ve used a cleaner that’s left any residue on the MAF sensors you’ll make matters worse.

I couldn't find an actual MAF cleaner, so I used an electrical contact spray from halfords which seemed to do the same thing. I was really careful and allowed it to dry properly. As far as I can tell, it hasn't made any difference at all.

In any case I took the car out for random drive yesterday and it ran beautifully for a good 40 mins, no issues at all. But then I stopped at Tesco and when I started the car, it was running rough again.

Sanchez · 3 Jan 2018 at 12:54

Could it be a leaking injector issue? You say it happens when the car is warm, stopped for a short while and then started again? Some reading I've done on this suggests it might be down to leaking injectors or HPFP. A copy of NCS Expert/INPA and a decent ODB cable should give you all the fault codes.

Lashout_UK · 3 Jan 2018 at 14:37

Sounds like a duff coil or plug, or just a poor contact between the two somewhere. You'll need a specialist to look at it, really.

Ali1996 · 22 Dec 2018 at 20:31

Problem fixed ?

Scania · 24 Dec 2018 at 11:18

Ali1996 said:
Problem fixed ?

It’s been nearly a year, why ask now?

fastwunz · 26 Dec 2018 at 13:54

Armageus said:
If you haven't already got one, it's worth picking up a Bluetooth OBD2 dongle, and a copy of Torque or similar for your phone.

With that you can monitor the various sensors, and may be able to spot the issue straight away (e.g. if there is no or intermittent reading on one)

This 100%