High tick-over

Q

I have a 2016 VW Touran 1.6 Bluemotion diesel – it’s done 104K and is on its original battery. Recently it’s developed a slightly high tick-over. This is a relatively small problem, but one I’d like to fix before I sell the car. From cold, the engine turns at the normal 850 or so revs – but when I get going this rises to around 1000 to the effect that I can get to 30mph in 5th gear – foot off the accelerator pedal. My basic code reader shows no codes.

I read somewhere that these engines, or the like, over rev like this to compensate for a weak battery – I don’t know if there’s any truth in this. The battery shows 12.37V, vehicle at rest. Also please, should I need a new battery – would this need to be coded in upon connection? Peter John Ayton

A

There is one problem that is common to your vehicle, although it does normally give a slightly different problem, and this is the throttle pedal connection between the harness and the throttle pedal itself. As this is quite a common fault, I would start by checking the connecting plug and terminals for any corrosion or joint problems.

If no problems are found in this area, then it would be worth checking the live data on the engine sensors, air and coolant temperature, etc., to ensure that the ECM is not receiving false information causing the rise in tick-over speed. I would also check the intake manifold air control actuator to ensure this is not sticking.

Other causes of the rise in tick-over speed such as an injection fault would normally give other symptoms such as excessive smoke and uneven running, so I do suspect this is a more likely to be a sensor which at some point is giving out incorrect information.

If the battery does need changing, there is no resetting procedure needed but the following process should be observed.

▶ Erase any trouble codes.

▶ Switch the ignition on, then wait 30 seconds before switching the ignition off again.

▶ The ignition can then be switched on and the engine started.

You will also find that the TCS/ESP warning lamp will illuminate – this will be extinguished after a short drive.