Thanks Daemon, and you're right, there are all kinds of noises coming from a diesel that I never experienced with a petrol engine. The problem in diagnosing this is that the car runs perfectly all the time I'm not on a long motorway run, which firstly makes me think there isn't any serious engine issue, and secondly makes it difficult for a garage to figure what could be wrong unless they can take it on a long run themselves. The other thing I should have mentioned is that even though this is a 2012 (manual transmission) car, it isn't some old, high mileage smoker, it's only 45,000 miles with a full service history

The next time you plan to take a long motorway run, mount a cell phone or Hero-type device in your vehicle in a location (maybe between the front seats at eye-level) that will record the engine's performance before, during and after the juddering. Then start your trip and press the record button shortly before you think the juddering will begin and, after the juddering starts, keep recording until it stops and the engine goes back to performing well. Hopefully the recording will not take long to view. If a photo is worth a thousand words, a video recording that shows the juddering very well to a technician's eyes must be worth at least a million. (After you make the recording, you can do some intelligent editing in order to shorten the video while still retaining the parts that show what's important.) After watchng such a video, I would not be a bit surprised if a technician said "I know what the problem is".

An alternative to the above might be to somehow borrow or rent a good OBD2 scanner/diagnosis device and have it connected to the vehicle and constantly displaying (some even record for later analysis) engine and other systems' performance during a trip that is going to be long enough to have the engine start juddering.. If you have a scanner that cannot itself record this data, you can use a video-recording device, pointed at the scanner's screen, to record what's on the scanner's screen. Then pay a technician to watch the video and see what he says.

Again, good luck. I hope you or someone else figures out what the problem is. If that happy ending happens, I hope you post here what the problem was.

Hi Outlaander, thanks again, and very useful suggestions. The garages I've had look at this have all plugged in their OBD2 diagnostic scanners but no faults are shown, but if I can get hold of a scanner myself your idea of running it live to see if anything pops up while the fault is occurring on the motorway is excellent. Failing that I'll definitely take a video next time I take a long run and post the results here to see if 'a million words' help diagnose this better.

Thanks and regards

Hi Outlaander, I went out for a drive yesterday so got the chance to try your suggestion of recording my engine. The first part of this clip is soon after I started and the car was running fine (at around 60mph), which it did for the next 20 miles or so. I then recorded, at the same speed, coming back when the juddering was underway. Unfortunately there was quite a lot of wind noise so it's difficult to hear (although you can see the video shaking slightly as the juddering starts), so I included another clip at a lower speed to reduce the wind noise.

Here's the link:


​​​​​​​Hope this helps

I must say that I could not hear the juddering versus not juddering, but I did notice a couple of things.

1. The speed shown in the speedo did not hold steady during juddering, but it did during normal operation. Did you use cruise control at all times, or was your foot controlling the speed?

2. The "mpg" indication in the center of the console was not nearly as steady during juddering as it was during normal operation. This may indicate a fuel-supply issue. About the mpg indicator, there are two visual represenations -- a solid white line and a green line. The white line does not move that fast, but the green line moves pretty quickly. What is the difference or relationship between the two lines?

As you mentioned in your first post, the big diagnostic problem you have is that you cannot make the juddering happen while a tech is attempting to diagnose the problem, AND that there is no fault code "check engine" triggered during this juddering. The latter is almost unbelievanble, but the fact is that there are no codes.

It would be nice if you could have an OBD scanner/bi-directional diagnostic tool installed during operation so that you could monitor, "live", various engine systems' data -- in particular the rate of fuel usage, fuel pump performance, coolant temperature, etc. I know that on some gasoline vehicles that have OBD2, each individual fuel injector can be turned on or off. This is very useful, for example, in diagnosing a rough idle or rough operation above idle. If the normal idle speed is, say, 900 rpm, and the vehicle is idling at 700, while still idling the engine, each injector can be momentarily turned off to see if that has any effect on idle speed. The one that is turned off that does NOT have any effect on idle speed is probably faulty. IF your diesel's injectors can be similarly turned off and on while the juddering is happening, one by one, maybe you can determine if you have a faulty injector and exactly which it is.

Therefore, as a next step that you can probably accomplish while sitting in front of a computer, you might want to determine exactly WHAT can and cannot be monitored and bi-directionally controlled via OBD2 diagnostic tools during your diesel's operation.

Thanks, once again, for a really thorough and helpful reply. Covering your first 2 points together, I fully acknowledge the juddering is extremely difficult to hear, especially with the wind noise. It's more obvious when I'm accelerating so when you saw the mpg indicator fluctuating when it did, that was because I was easing off the throttle and then depressing it again to try and make the juddering easier to hear. While this made the juddering slightly clearer there was the obvious knock on effect that the mpg was going down. In answer to your question about the two lines on the mpg meter, the white line shows average consumption over a period of time and the green line shows instantaneous consumption. So if you briefly floor the throttle the white line will be unchanged but the green line will shoot downwards; take your foot off the throttle and the while line will again be unchanged and the green line will head for the far right hand side.

I'll look more into seeing if I can get hold of an OBD scanner, although to get a decent quality one (it looks like the cheaper ones only pick up on a subset of codes, so may not help anyway) may be difficult or more expensive than I can/would pay, or would require me finding a friendly garage to loan me one. Anyway, I'll definitely look into that.

Thanks again for all your advice, and if anyone else has any further information on my original question regarding the MAF sensor, that would also be really helpful.

Did you manage to sort this?

No, sadly the fault is still there and the assembled might of the RAC, local garages (3 times) and Mitsubishi main agent (twice) have been unable to identify the cause. I did buy an OBD scanner and eventually that showed up a P0102 faulty MAF sensor so I changed that, which did seem to improve the fuel consumption (so I'm guessing there was a fault there, just not the main cause of my problems). I was hoping that maybe the duff MAF sensor had been causing the car to run too rich and that had clogged the engine up so put in some STP Ultra 5 in 1 diesel cleaner but that doesn't seem to have made any difference either. So still stumped I'm afraid: no engine fault lights on, no fault codes showing on the OBD scanner, but the engine still starts to misfire after a 10 mile motorway run.

Mine does too. I’ve replaced everything. Took the boost pipe off between the throttle body and the intercooler yesterday and where it joins the intercooler was covered in black soot. So it’s leaking there. I tightened the jubilee clip and now it misfires slightly differently and no where near as bad. (Dropping to 4th before helped) now dropping to 5th is good. So I’ve ordered a stronger hose clip for both ends.

try checking that. It doesn’t leak much boost until it gets hotter and past 15psi of constant boost load like on a motorway.

Mmmm, interesting thought, thanks for the suggestion I'll give that a try over the weekend