I have just had this happen to my car - happened over the Christmas period so only just gone into the garage.
I broke down on the M27 - a light came on which is in the manual as a water in the diesel light in the manual, however my car is a petrol. The garage tell me this an engine management light. Basically when the light came on i really started to lose power, i managed to limp the car over to the hard shoulder and await the RAC.
When they came out they had a look and told me it was my head gasket - i have had a look, dont know much about cars but cant see the mayo stuff they spoke about anywhere.
The garage have said they cannot find anything wrong - no errors in the diagnostics, and they have taken it out and seems to run fine.
When i took it to the garage it felt awful - i didnt push it above 30/40 because the car didnt feel like it had much more to give.
Sometimes, when i accelerate it feels like sometimes the power drops for like 1 or 2 seconds, and then returns - almost like lurching you forward as if you were just taking your foot on and off the gas.
As i type they have just phoned - only a few intermittent errors showing, nothing perm -errors were things like
They have cleared down the errors and asked me to drive it round again and see, but I am a bit worried, i commute each day and am terrified of this happening during rush hour with no warning
Any help would be great - oh its a 2003 1.2 16v renault clio with about 100k on the clock - yes i should get a newer car!