Throttle problem

I have a 2007 VW Polo GTI 1.8T with a BJX petrol engine, a Bosch fly-by-wire throttle pedal and 20,000 miles on the clock. The battery is fully charged via a smart charger.

I had no problems until after the prolonged spell of cold weather last year, during which time the vehicle was used intermittently. It starts and drives normally, with zero fault codes displayed by VAGCOM, but idle speed sometimes stays as high as 1100rpm and sometimes drops to normal rpm, even when the coolant is at operating temperature. Lifting the throttle pedal with my toe instantly reduces the idle speed to a normal and stable speed. Lifting the throttle pedal by hand does not reveal any obvious play – the pedal appears to be hard to its rest position

– and ’snapping’ the throttle closed generally overcomes the problem.

I am assuming this is not a problem with the throttle body stepper motor, because of the pedal-lifting effect. I am considering removing the pedal assembly in order to spray contact cleaner on the resistance tracks and associated contacts. Having spoken with a couple of AA technicians, they both suspect the TPS has become sticky, but are surprised the fault is on such a low-mileage vehicle – they generally see incidents of irregular idle speed on much higher mileage vehicles.

Please could you advise on the following: 1 Could you confirm this is most likely

a fault in the TPS?

2 Should I use an ECU memory saver device and disconnect the battery before removing the TPS, or would it be safe to just unplug it?

3 Can the TPS be dismantled sufficiently

to spray with contact cleaner?

4 Should I just renew the TPS assembly at

a cost of around £100?

5 Am I correct in assuming the TPS is not

coded to the ECU?

6 Is this a common problem?

Rob Packham

In answer to your first point, given the tests you have already carried out, the problem is most likely the accelerator pedal position sensor, as you suggest. The operation of the throttle does not have a direct connection to the position of the accelerator pedal and final control is taken by the vehicle’s ECU. The throttle pedal position sensor

is not a serviceable item, but it would be worth making an attempt to clean the unit before considering replacement. The unit is not coded so there is no need to worry about coding, and the unit can be safely unplugged with the ignition off. Unplugging with the ignition on will throw up a fault code ‘G79’. I would try to clean the unit by flushing it through with an electrical contact cleaner spray. Allow it to dry before refitting and testing the operation.

Although not a common problem, failure is not unheard of. But, as the AA technicians you spoke to confirmed, the mileage on your vehicle is low for this fault to occur.