The first batch of v piwer nitro had a cleaning agent in it that has since been removed, I phoned shell as I had 3 det codes 10 minutes after brimming it with the stuff, shell advised me to put in octane booster as I may have got regular unleaded in the pump but theu couldnt gaurantee it, I ended up doing so and car returned to normal, 2 weeks ago my mrs went to tesco and put 20 quid momentum in and the car did the same check engine light and wouldnt rev past 4000 rpm, so I think its just down to whatever is in their pumps that would cause bother,