Lambda light.

[wacky racer]

I was on the M1 a couple of weeks ago, and came up behind a slow car so i pulled into next lane and gave it some stick.
As i did this the Lambda light came on.
It has done this before on a motorway, had the code read and reset but i lost the piece of paper with the code written on!!
Car also hesitates slightly under real hard accleration.
What to you guys think, air leak?
Mark.