I would suspect this is a fault with the electronic throttle body which seems to be a common problem area on models with the gdi engine.A good clean may fix it.If not,then an overhaul will be required.hth

did it also fell lumpy? i have just got a y reg pinin, and it went wrong the other day, and felt like it was running on 3 cylinders. Got it to the mechanics, and one plug was covered in black coroded stuff. Got new plugs and all ok, but the day after, it has gone back to nearly the same...vibrates when reved, sort of like its on 3 and a half cylinders, but its got a bit more power than when one of the plugs was knackered. It idles at just below 1000 rpms, and then drops to 200rpms, few secs later it goes up etc...

Would the original posters solution be mine?

thanks

just been reading about the fuel sensor, and the throttle body Carboning up, so i will give that a clean tomorrow, see if that helps.

I have same experience and worse but slightly further down the line. Bought Pinin 2.0 in Jan 2011 and has run fine since but a tad thirsty and sooty round the exhaust. And then ...

Suggest you sit down first and type Mitsubishi GDI engine problems into Google and then take a deep breath as you start to feel sick. Basicaly they get carboned up but you can read the whole sorry history about the why on google. My symptoms more or less amae as yours and came on overnight and stayed. Undriveable. Ecotek Powerboost down the inlet didnt work (expected but worth a try as its low cost). Am currently having the throttle body reconditioned (£250 all in by ECU Testing Ltd - BBA are another alternative - both have websites). I was not obviously carboned up badly but the moving parts were very gummed up and part seized. It could not have been metering air correctly

When this comes back i hope it sorts things but I'm half resolved to trying the Mitsubishi walnut shell decoke after that for the inlet manifold and inlet valves that aslo coke up. This treatment is well documented on Google too. Not cheap and you need to go to a Mitsi dealer. If that does not sort it I expect to be £700-£800 worse off on a heap of **** car that cost me £3500 and will be jumping from a bridge. As a last resort I may pull the injectors and replace with remanufactured units. Other wise too much good money is being thrown after bad and despite being a lovely car in great condition the scrapyard beckons! Not Mitsubishi's finest hour. The engine was aslo fitted to Volvo V40 so dont go after one of them!!