ah right so its only when the electronic choke is on (high idle) then they go back to normal tricky one

I'd want to measure current draw at the same time as the voltage drops to see if any consumer is drawing excess currrent at the same time as the voltage drops.

Does it do it with the heater blower / aircon turned off on cold start ups?

Does the auto tensioner run smoothly? Does it kick / jump when the voltage drops? Does the aircon pulley engage when the voltage drops?

Is the main battery to body earth strap in good condition? Connect a good quality jump lead from the engine block to the battery neg and see if this helps.

Dox, I'll check that the garage has done all of your suggestions thanks. It does seem to do it under any combination of electrics being switched on and anything mechanical- belts, tensioners, pulleys etc. are all fine.

Well this morning just to satisfy my own curiosity I unplugged the secondary air pump. First cold start... no issues, no voltage drop. It is way too early to start counting my chickens but it is a good start!

EDIT- Forgot to say thanks to Rob Clubley for the PimpMySkoda guide as the pictures on there made it a piece of cake to locate the pump.

Edited 7 January, 201214 yr by lordrobs

Sounds like the SAI pump is seized up & drawing a lot of current hence your lights going dim. A lot of people remove the SAI as it's not essential.

Did the cause of this problem ever get found? I have similar simptoms with my octavia vrs. But lights slightly dim intermittently all the time hot or cold. I'm thinking rectifier but can't be sure. Sometimes it can be ok but others it can be really distracting. As I am sure you are aware.