We once bought a 118k mile passat, think it was something like a 1.6 petrol at the time. It was a minter but had no go in it. seems the owner had done a 100k in it never going above 40mpk.
I drove it back to the workshop about 7/8 miles and there was just no performane to it.
We tool the plugs out and measuered/poured redex down the plugs holes, hand cranked it to coat the bores and set the crank so the pistons were at half way down the bores, then toped up wuth measeured ammounts of redex and left to soak overnight.
Day after we put the rest of the redex in the =tank and pouered a gallon of fuel in to agitate the redex.
Battery connected and turned the car over a few time to clear the bores the best we could, plugs in and start the car, when it finally started there was a thick grey cloud fill the workshop as all the crap was burnt off the inside where the redex had been. Quick run round the back streets till the smoke cleared and fault find the car. Full service, full valet, we ran it for 2 weeks and it was such a sweet engine once it was cleaned out, shame to see it sold, but it doubled it's money and the guy came in for a fortnightly wash/polish for quite a while after that and the odd service.