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You have a choice of Abbey in the south or RSTuning in the north (Leeds). Most people have seen a small improvement in MPG judging by what I've read.
I am very interested in this also, but am very of letting someone carry out work on the car. Abbey get all the comments on here regarding the uprvs etc, and very little said about RSTuning. I am Bradford only 10 minutes from Leeds, so RSTuning would be my first choice due to been local. Are RSTuning in the know with the 350 has Abbey are??