I cleaned up my egr valve on my PD140 Altea last week ( it was filthy after 47k) and made up an ally plate with 4mm hole to reduce the egr and after less than a week I have a CEL. My driving is mostly town work, so I don't know if that has a bearing. I really wanted this to work, as the soot is probably responsible for all the crap in the egr and anti shudder valves that i had to clean.