1.9TDI revs to red line when starting after cold night

[ChazzyB]

The title says it: My wife's '07 plate 1.9TDI Roomster has for some while had this somewhat worrying problem. If the night has been freezing-level cold, when she starts the car, it will rev to the red line and sit there. Needless to say, she will immediately switch it off. This will happen two or three times more before it will (so far) eventually start properly. 

 

Any ideas where and what to start looking for?

[aubrey]

The fact that it sits there suggests to me that the revs are being controlled. The engine is not running away.

If it was my car I'd confirm the accelerator without starting the engine, Engine - 01 - Measuring Blocks - Group 1. Does it go 0% to 100% as you press the accelerator ?

[SurreyJohn]

My hunch is the accelerator pedal.   Not sure if it same on that model, but there is a potentiometer (an electrical device) that pressing the pedal moves.

 

Sounds to me like it has short circuited and instead of getting a build up as pedal is pressed, going to full power whatever the pedal position.  Might also be pedal and electrical linkage is broken, so as pedal comes up not reducing power.

 

 

[Robjon]

Aubrey's and John's posts have jogged my memory.  I have a vague recollection of posts made on here in 2009 (the year I bought my first Roomster) that suggested some potentiometers fitted to 2007(ish) Skodas were failing prematurely. So if my ageing memory has served me correctly, it would seem the potentiometer is a known weakness.  Again from memory, it is a reasonably straightforward and inexpensive fix.

[ChazzyB]

Thanks for your suggestions. I'll take a deeper look.

 

Still a bit odd that the only time it does it is when it's very cold. Otherwise, it's as good as gold.