Why does my car run rough sometimes?

titaniumx3 · 22 Dec 2017 at 20:44

I've had this issue to some extent with the last three cars I've owned but its the most pronounced with my current car a BMW E92 330i (N53 engine). When I start the car cold in the morning, it runs beautifully, buttery smooth and tight, and the engine/exhaust makes a clean howling noise. However after it's warmed up or I start it again after driving for a while (say 20 min), the entire character of the car changes, the engine now feels rough when accelerating, and makes coarse exhaust noise. The effect is worse when I am driving slowly in town and even makes a rattle/grinding noise when accelerating from lower rpms. It sounds a lot like a diesel van. It's hard to say if the actual performance is being affected, but it certainly does not feel as good to drive, nor does it sound half as good.

Now the bizarre thing is that this does not happen when it is wet outside. When it's raining the car feels consistently smooth. I can even take the car for a wash and it will make all the problems mentioned above go away, until it has warmed up and dried again of course.

I've taken the car to multiple garages and they all say they don't notice any problems and that the car is working as it should. Some of them say that this is normal for BMW cars. I don't know if this is true as this is my first BMW. I've looked into possible issues with the DMF, clutch, propshaft mounts, but nothing is conclusive and all the garages tell me all these items are in good condition. It's honestly driving me mad at this point, as I really enjoy driving the car when it's working smoothly.

I would appreciate some advice on this. Is this a common problem? What is causing it?

titaniumx3 · 22 Dec 2017 at 20:49

dholdi said:
Do you live somewhere with a warm climate ?

No I live in the UK.

titaniumx3 · 22 Dec 2017 at 20:57

dholdi said:
Ok, I would take a guess at fuelling being incorrect if it runs better when its cold.

I've always use either Shell regular unleaded or their vpower stuff, it makes no difference, same issues. Unless you mean something else?

titaniumx3 · 22 Dec 2017 at 21:05

Scania said:
Try replacing the MAF (mass airflow sensor) with a known good one, I’d put money on this being the culprit.

My old 328i e36 did exactly this, replacing the MAF cured the rough running - and transformed the car.

I did read about this once, but didn't think it would cause such a huge change in how the car runs.

One other thing I've noticed is that when the car is running rough, if I rev the engine at idle, it makes this weird 'swirling' or 'swishing' noise after each press of the accelerator. It's hard to explain in words, but it's like air is leaking from a pipe or something. I doubt this is what is actually happening, but it kind of sounds like this.

titaniumx3 · 22 Dec 2017 at 21:07

Armageus said:
is it fine at full throttle (i.e. rather than just gentle acceleration)?

During cold start/full throttle the engine runs "open loop" monitoring rather than relying on Air flow and Lambda/Catalyst sensors. As above MAF sensor, or even a dodgy temperature sensor could cause this.

Yeah, the higher I rev the engine, the less notice able it is. I also can't notice any difference when cruising on the motorway, it's just when driving in town.

titaniumx3 · 22 Dec 2017 at 21:16

Is it is easy to change the MAF sensor? Where is the best place to get a replacement part? I'm a bit useless when it comes to car maintenance.

titaniumx3 · 31 Dec 2017 at 03:01

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.

I still have no real clue as to what the problem is, but I suspect it is an engine problem as I can notice a definite change in the engine noise even when revving in idle. I also feel that performance may be degraded when its in this 'rough' state. I also know that it has something to do with temperature and humidity, car runs smooth when it is wet outside.

Another thing that I've seen happen is that, when the car is running rough, if I turn it off, wait a minute or two and then restart it, it's running smooth again. I did this yesterday and after restarting it, the car ran smoothly for remainder of the journey (about 35 miles), plus it wasn't wet or damp outside, just cold.

I'm not sure what to do, other than take it to another garage. Anyone know of somewhere good in or around Essex?

titaniumx3 · 31 Dec 2017 at 03:04

[Ignore]

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?

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.