My Vw 1.8 Tdi always gets a good reving, up and down over the moors. never any problems until last week. Had been running fine that morning, pulled in for a butty. on pulling out in traffic, very long line. lost power. Duh car behind rather close. No power at all Limp on to where I was going. Going home OK. A few days later fine going out on return about 30mls from where I was, went to pass a truck. Power gone again. Did not know about the switch off on bit, which I have tried since, and works for a time. Put some cleaner in as some one suggested. Going up one hill it drops powere get to top off/on OK next hill not bad further along, had to brake hard, ( A line of Ducks, walking across the road. they didnt, Duck that is. one lost iys head) as I braked the display bleeped and emmissions Workshop came on display. Slight loss of power, tried running at high revs for some parts after that. still lost power, after a few stops off/on managed to get where I was going. later display still had error. a few hours later started without error. seems fine since, but reluctant to test fully just in case, But I know I will have to. Assume the emmisions came on as maybe some rubbish from the system came loose, helped by the additive. Will wait and see