jumping rev counter when idle????

[crazy-steff]

hey all, got home 2day and could here my engine gently reving by its self!! took a look at my revcounter and it was jumping from about 500rpm to about 800rpm..... anyone had this problem or know what causes it?
cheers for any help.

 

[TheOtherSimon]

Hunting idle is a common problem. Do a search.

To start you off, it is often caused by lambda sensors, MAF or temperature sensors.

Simon.

 

[crazy-steff]

cheers, will see what comes up!!! do u have any idear what will happen if the problem is just left???

 

[usernametaken]

I might be wrong but it might be the timing belt, how many miles has it done? My last car did the same just before it had the timing belt changed and after it was replaced it was fine.