S40 T4 issues

Hello Everyone,

I have a problem with my Volvo S40 T4 1997 UK model.

The trip computer petrol gauge will keep resetting, e.g. after driving 80 miles, all of a sudden it will reset and show I can drive another 500 miles! and the gauge will show maximum bars again. After driving a few miles it will return back to return range again.

Also once a week or so, the car will idle very erratically after city driving. At a stand still the engine will rev from 200rpm to 1500 rpm by it self, only way to stop is rev the engine to 5000rpm. At the same time if I drive the car while this is happening the car will feel like it wants to go backwards, whilst making a clicking noise from the engine.

Any idea what this fault could be, I have warranty for the car which runs out on Oct 10th so want to get any car problems before this?

A few months ago I took the car to the dealer to fix this problem and another where they could not reset the service light, their computers could not communicate with mine. They changed the ECU but it did not fix the problem so took it out, After having the car for 3 months they worked out it was the alarm control unit. This seemed to have fixed all the problems, but the trip computer and idle fault has returned.

Any suggestions would be appreciated.

This is a difficult one.

The first thing to do is write a clear letter to the dealer stating the problems exist before Octobre 10. Provide for some acknowledgement the dealer got your letter (I'm not familiar of the possibilities in your country and I don't know how this "acknowledgement" is called). The second thing to look for IMHO is: "is there anything disturbing your computer?" and "is there anything disturbing the communications between the ECU and the dealer's equipment?". The whole circuit between the battery and the computer could pick up some noise like fast voltage fluctuations. This noise could influence the computer.

Therefore I suggest to check:

- *all* connections to earth (the metal of the car)

- the battery

- the circuits directly connected to the battery such as the generator and the wiring

- the circuit breakers