This one has me and the garage stumped, so hopefully somebody on here might give us a steer, ( sorry it's a bit of a shaggy dog story ) :

The car is a 55 plate Octy 2, 1.9 diesel, owned from new, maintained on the service schedule, and now at about 128k miles. Up to mid Sept this year it has never let me down, but then I got the engine warning light, so booked it in at the local VAG independent for 2 days later, to check and possibly replace the EGR valve. On that day there was heavy rain and part way to the garage the car spluttered and died, and would not restart. I called the RAC, and surprisingly the car was fine by the time the patrol arrived, and it drove without fault to the garage, who replaced the EGR. That evening, on the way home, the 'coil' light came on, indicating a possible issue with the glowplugs, and again the car died and took about 5 minutes to restart.

Next morning the car started but after about 2 miles spluttered and died again. Again, after a few attempts, it decided to start and I drove it to the garage who said to bring it in tomorrow - when I do the diag suggests a fault with one of the engine speed sensors. They clear the fult code and I will drive it around to see if the fault comes back. 4 days later it does, with a vengeance, I start the car and only get about 30 yards before it dies, and refuses whatsoever to restart - even if it fires, the moment it's put into gear it cuts out. I finally get it back home in reverse, it flatly refuses to drive in a forward gear. Again, there is very heavy rain.

Next day the car is fine and I leave it at the garage, who later in the day ring to say they cannot find a fault. 2 days later, in heavy rain, the warning light comes back, as does the stuttering, so back to the garage......

And so it went on: drives fine for days then splutters and dies without warning, and takes many attempts to get going again. On one day, it took about 20 attempts to get it far enough from home that I could consider calling the RAC recovery - but just as I gave it one last chance it burst into life and drove perfectly to the garage, where once again no fault could be found. On another day a couple of weeks later, in heavy rain, I did get the RAC out, and his diag unit showed 2 possible faults and he was concerned that the timing belt had slipped if not broken. The car was again left with the garage who even 'soak tested' it by going twice through a car wash, as the fault seems to occur when there is heavy rain, but again it refused to misbehave when they looked at it.

So far the EGR valve, glow plugs, and both engine sensors have been replaced, I have also switched to using the spare key in case the immobiliser has 'forgotten' about the coding on my normal key.

Two weeks ago it had what I hoped was it's last visit to the garage. However this evening, about 500 miles of driving later, ( and when it is raining ), and at 30 mph, there is a splutter, a cough, and the engine cuts out, ( this is 1 mile after filling up, so it hasn't run out of fuel ! ). Ring the garage who say that the best bet, due to the time, is to get it recovered home and see how it is in the morning. Ring the RAC, who say they may be about 2 hours, so after about 20 minutes I try to start the car, which fires for about 2 seconds, then dies. 10 minutes later, however, it starts, and gets me all the way home, ( about 15 miles ), without a stutter. So now it's going back to the garage tomorrow morning.

My gut feeling is that it's electrical - it only seems to happen when it's raining. I have looked at similar threads and am certain that, for instance, there isn't an issue with the rear brake lights, which seems to have some connection to the engine management circuit. Could this be a fuel pump problem ? Whatever it is, why so intermittent ?

Have you checked if the main fuse box under the bonnet is wet?

Other possibilities are that water is getting past the windscreen and into the wiring and control modules behind the dash.

Does it have a sunroof?

Does it have a sunroof?

Yes

Do you know what the codes were?

My guess is one of the faults was

17748/P1340/004928 - Camshaft Position Sensor (G40) / Engine Speed Sensor (G28): Incor. Correlation

Whilst in theory it could be a timing problem, my guess would be a faulty Camshaft Position Sensor or Engine Speed Sensor or the wiring.

If you're getting dd glow plug errors and you're sure they are fine, then check the glow plug and injector wiring looms. The it in hot oil, which can degrade them.

Did you ever get this sorted? I have EXACTLY the same symptoms when it rains with my 2006 Octavia with 112k miles . Skoda dealer replaced glow plugs and cam shaft position sensor but still cuts out when wet!!!

RedRoseSaint hasn't logged in to Briskoda since 8 December 2012 so a response is unlikely. :(