Car Doctor: Why does my diesel Mondeo cut out?

Q. My 1982 BMW 320 won't idle properly when cold, and when I accelerate, it judders. What's going on?
Chris Nicholl, London

A. There are a number of faults. It could be an air flow meter which is on the blink, or a failed coolant temperature sensor. The sensor does what it says and supplies the car's electronic brain with information about the engine's warmth. With cold engines, they need more fuel, so out comes the choke. When it fails, the engine either doesn't get enough fuel, so it runs roughly when cold, or alternatively it gets too much. That could be the source of your rough running.

Q. I have a diesel Mondeo that runs very well until the fuel level drops low. It becomes harder to start and sometimes cuts out in traffic. I'm getting really annoyed by it now.
Rob Earnshaw, Carrick

A. It could be the sender unit and your gauge may not be working accurately. These are simple items that any garage should be able to check fairly quickly. Many cars, however, have what is called a lift pump in the fuel tank. This takes the fuel from the tank to the main injection pump. If it fails the car will still work, but when the level drops the main pump can't cope. So if you have a full tank and it starts easily then it is probably be the lift pump.

Q. The digital odometer in my Volvo has gone a bit bonkers. It counts upwards in random amounts and sometimes even backwards. What can I do?
Alison Barry, Ludlow

A. Your mileage chip is probably on the blink. You will need to consult an auto electrician to find out where it is. On early cars with the digital systems it could be part of the loom, while on others it was part of the instrument cluster. If it bothers you then get a secondhand item from a salvage yard. Get a quote for fitting it, however, as the cost may outweigh the benefits.

Otherwise, guestimate your mileage for servicing purposes. I ran a car with temperamental odometer for two years and managed perfectly well.