hi all, recently my 02 155,000 mile doblo jtd has lost seriuos power. it wont go over about 60mph and the acceleration is very poor. going uphill is a nightmare it goes like a slug. i went to my regular mechanic who said it might be the air flow meter. he replaced it with a new one and no difference. when the meter is unplugged it goes like a rocket but with plooms of black smoke from the exhaust. i took it to my local auto electriciasns whom after 4hours work and a cost of £80 was told it was the waste gate valve. i went back to my mechanic with the diagnosis and he stripped it out replaced it and still the same. can anybody suggest anything before i waste more money. thanks a frustrated geordie taxi driver.