Can anyone out there help me . I own a skoda Octavia 1.4 and in the past couple of weeks every time I turn on the engine it revs by itself jumping from 500 to 1000 revs and back again even causing the lights in the car to dim , I hooked up vagcom to the engine and no faults were reported as well as cleaning out the air filter and housing. Any help would be much appreciated.

BYRNEMAK,welcome to Briskoda.

Not sure exactly what's causing your fault -- few things come to mind -- have you tried removing the battery for 60 Seconds -- this is like a basic reset - sometimes will clear any glitches.

1 other thing to check - make sure your throttle cable isn't too tight.

Then you are into more complex item's like lambda probe,temp sensor,cam sensor etc.

Does it only do it when cold or will it do it when the engine is hot also ?

Does it only do it for a couple of minutes or the whole journey ?

Have you changed fuel's recently ?

Have you had flat battery recently ?

Thank for the reply Dave , you mentioned some interesting points. It appears to only do it when it is cold and only for the first couple of minutes , once I am on a journey I have no problems when I need to stop at traffic lights or any other time the car is in neutral , also I got it serviced last week hoping that the mechanic could fix it (Not a skoda dealer mechanic) , but he reckoned that it was an electrical problem and that I should go to the skoda garage , unfortunately when I rang the skoda mechanic he told me he couldn't fit me in until the end of August but he did ask me questions over the phone regarding the battery.

Ok you could try discon the battery -- make sure you have your radio code 1st tho,but I suspect 1 of the coolant temp senders is going pete tong -- won't always show a fault on diagnostic.

It's a fairly common problem -- but the good news is that a coolant temp sender is fairly cheap probably around