Faulty MAF Sensor?
 

I posted a message a while ago about my 2012 Outlander juddering at around 70mph when on a long motorway run. There were a couple of suggestions on here and I've been to three different garages, including a Mitsubishi main agent, but nobody has been able to pin down this fault. (I think a lot of this is down to the fact that it's not showing an engine management warning light and no error is coming up on their diagnostic machines; these cars are so complex now that if the fault doesn't show up on the diagnostics, everyone's lost.)

So, this juddering happens at around 1800-2000 revs, about 70mph, after a long run (say 30 miles+) and seems to be accompanied by a faint whooshing noise. The car runs perfectly sweetly at all other times so I don't think it can be injectors, turbo or similar, so my latest thought is one of the engine sensors that can't properly manage the air flow mix as the car heats up. Most likely candidate here is probably the MAF sensor (but are there others I should consider?). I've taken it out and cleaned it using a contact cleaner but that didn't make any difference and I tried disconnecting it completely but the engine wouldn't rev past 2,000 so I couldn't try a run like that. Is it possible these symptoms could be pointing to a duff MAF sensor or would that show up on the diagnostic machine?

Any suggestions on this MAF sensor idea would be much appreciated, or indeed anything else that could be causing this.

Thanks all

Please describe "juddering" more precisely and exactly WHERE you feel it (steering wheel, seat, lack of normal accelerator response, does cruise control work normally and vehicle hold exact set speed going up hills, etc.)

Thanks for responding, and for making me realise that my description of juddering was pretty non-specific. So, in answer to your questions, the juddering is engine related, certainly not wheels out of balance. I feel nothing through the seat or steering wheel and until I've been driving for over 30 or so miles, motorway performance is perfectly OK. When the juddering kicks in I can accelerate OK and I can drop down a couple of gears and that helps a little. Interesting question about the cruise control. I've never tried that since our motorways are rarely quiet enough to think about it, but if that would be an additional pointer to a possible cause I could certainly try it.

I still don't know what you mean by "juddering". Let me put it differently. How can you tell that the engine is juddering vs not juddering?

Best way I can describe it is if this was a petrol engine rather than diesel, I would say it feels like it was misfiring. So when this 'juddering' starts the engine is running very roughly and won't pull

Your surprised me with your statement that you have a turbo-diesel, so I read your first post again and now I see "turbo", so I guess I should have figured out that you have a turbo ............... which means, unfortunately, I can't offer any suggestions as to what's causing the "juddering" other than to check your fuel filter and fuel pump, because your description of the problem seems to me to be fuel starvation or one or more cylinders losing compression (but it seems to me that the latter would affect preformance at all times, versus filter plugging or inefficient fuel pumping). If I were you, I'd replace the fuel filter right off the bat, just to make certain that it is not the problem. (Do you add diesel fuel's equivalent of dri-gas to your tank once in awhile? When I owned a naturally-aspirated Mercedes 240D with 78 big hp, I found that doing that was good practice all during the winter months.)

Good luck.

Being turbo, test for any boost leaks and make sure all the intake pipes are tight?

Thanks for your help and suggestions Outlaander

I think the garages have tested that but if there was a leaky pipe wouldn't that result in poor performance all the time?

Diesel engines have all kinds of noise and that's normal. Not tight pipes, hose leaks may result in black smoke, loss of power but not noise, i doubt it.
Bad compression in one of the cylinders may couse some disbalance and vibrations.

There is a balance shaft and some parts, if weared out, may cause noise.

Automatic transmission, if faulty, may cause noise/vibrations at certain speed and gear. Yes, it is difficult to diagnose.