As 166 says, my case is probably worse case scenario with clogged DPF.
On this 2nd 159, I've needed new injectors, perforated manifolds, forced DPF regen twice, new sensors, engine resets/updates etc basically a new clean exhaust system. This has had knock on effects. Wild stuttering, surging on full boost, oil leaks, crank shaft issues and 2 sets of swirl valves (probably not blamed on the DPF, but that kind of hesitation 'off and on' boost in rapid succession does no good to an engine's working parts!)
I don't drive slowly, as some of you can testify first hand and I drive all over the UK motorways at semi-legal speeds, so in theory I have sampled most of the UK's fuel quality. My journeys are often long, sometimes 5 hours non-stop at high speed, but yet it still clogged. Really wierd.
My many many limp modes caused by DPF clogging have happened in different geographical places with different fuels. BP, Shell, high cetane, normal cetane, forte diesel additive, redex additive etc etc etc and there seems no pattern what so ever.
So in a typically long winded way Rick, I don't have a clue why
Perhaps someone should make a poll sticky and we can test Fraser's theory.
Having said that, I agree with Fraser that a disproportionate number of 159/Brera/Spider owners come onto AO to report problems and whatever results we get can't be classed as gospel.
Would be interesting though