hi, i'm new to the site.... I've been scouring the net to try and solve a few problems with my audi 80 tdi 1994. I tried to run it using bio-diesel which worked fine. Then recently my car began to lose power completely when ever i took my foot off the accelerator or pressed the break. It never cuts out but there is nothing there when pressing the accelertaion pedal after breaking. I have to put my foot down on the clutch and release it again to kick start the acceleration again. When the needle comes down to around 100 revs it makes a clunking sound and suddenly the power is back. None of the local garages can help. I changed the fuel filter and ensured the air filter is ok but still the same. It's quite dangerous when driving at high speed on the motorway, when you put it into 5th gear sometimed theres nothing there. the next thing you know theres another car up your behind flashing you and abusing you!! Just wondering if anyone has any suggestions please, as i'm up against a brick wall with it. Also lately i've encountered another problem where the boost pressure regulator or electric/vaccum change over valve is making a really fast ticking sound whilst i'm waiting for my heat plug light to go out prior to ignition. The engine turns over fine but doesn't start up. I try it again later and the clicking has somehow stopped and it starts 1st time. I paid for a diognostic check and it came back fault on the change over valve. After having a new 1 fitted i've found my car is still doing it, ticking and not starting. PLEASE, PLEASE, PLEASE HELP ME WITH THESE PROBLEMS. THERE MUST BE SOMETHING I CAN DO? WHAT IS CAUSING THE CHANGE OVER VALVE TO CLICK? AND WHY IS THAT PREVENTING MY CAR FROM STARTING UP?