My recently purchased (6 months ago) 2014 i30 Elite diesel (6 speed manual) seems to have developed what I hope is a minor issue, but will probably end up costing me a fortune. About 2 days ago I was driving it and it suddenly seemed to me to be a bit sluggish (It's no performance car, but I haven't had cause complain) and it was like that until this morning. I'd just convinced myself that I was imagining it climbing a particular hill on the highway in 6th gear with no problems and I must have been changing down to 5th gear without noticing, when bugger me, it climbed the hill in 6th with no problem at all. A bit of investigation and it now seems to perform perfectly fine and the sluggishness of the last 2 days seems to be a thing of the past. In the intervening 2 days I've done nothing which might have remedied any issues. I haven't even lifted the bonnet, haven't refuelled, nothing. When it was sluggish it still ran fine, no vibrations, no smoke and no lights on the dash, nothing to indicate anything was amiss. The nearest I can imagine was it was either lacking a bit of boost or a bit of fuel, but whatever it was it affected all 4 cylinders because it still ran as smooth as ever. Is this common, or should I engage the services of an exorcist?