Revs jumping

[Peter_HMR]

A friends B5.5 has erratic revs. When driving the car and coming to a junction and slowing down the revs will sometimes just take off and start increasing all on there own. It can also happen when starting the car the revs will jump away up.

Does anyone have any suggestions as to what it may be. I dont have a chance to scan the car at the moment but will do so as soon as I can.

[martin1810]

Common reasons for this are faulty clutch or accelerator pedal switches or more likely, problem with coolant temp sensor. I guess your scan will be of more help.

[Peter_HMR]

Thanks Martain what causes the problem.

[martin1810]

The engine ecu has a number of feeds that effect rpm. So an intermittent fault with the water temp sensor can lead to the rpm going up and down. Similar thing can happen with a faulty accelerator pedal but this usually sticks at a slightly higher rpm. Clutch switch fault usually causes a slight over rev during gear change.
Faulty fuel temp sensor acts like a faulty water temp sensor. A faulty map/IAT sensor has similar effects. So you can see why a code read is the most effective way to go. Too many possibilities otherwise.