After a series of issues with my Octy spanning nearly two years, it's now hitting make or break time so I'm appealing to see if anyone knows how to get their hands on diagnostic material that might make the difference.

I've had an intermittent fault that's attributed to angle position sensor 2 in the throttle body being 'implausible' and there's no way of triggering it on demand. We've replaced the throttle body, only for the error to come back within a few weeks, stripped it down and cleaned all of the tracks whilst checking the internal connections, checked all of the plugs, and patched in a replacement wire with fresh connectors to the ECU to bypass the existing one. Nothing seems to make any difference. The Skoda main dealer reset it once during a service and must have done something different because it stayed fixed for just over a year, but it's now back and being a pain. The only thing left is the ECU but I don't want to go there if at all possible.

What I'd like to know is if there's a document anywhere that explain which inputs are compared, and how, for a particular error condition to be set. I can't see any way of reasonably checking the possibilities if it isn't clear which components are involved, and I dislike the VAG approach of replacing major components on the offchance that they might be to blame. The only thing we haven't tried is to open up the ECU and check if the connections to the board are sound, but that's a last ditch measure. If I knew that the calculation involved a straight comparison with reference to the voltage across parts A, B and C to check they all fell within range D, for example, that'd be a start.

Any ideas would be hugely appreciated because I really don't want to sell the car, but impending insanity might force me to.

The only other thing I can think of that you haven't mentioned is the throttle pedal maybe. Sounds pretty bizarre.

You may be able to get hold of a de-immobilised ECU, and give that a whirl to make sure it's not the problem. Contact Shark Performance, as I remember Ben mentioning he could help with this.

What running problems does it cause you?

You could always convert it to the older cable throttle design! The older 1.8T Octavia's had cable throttles, so all the correct hardware exists for the car. Maybe a bit extreme.....

i think it is more to do with the resistance. can sometimes be caused by earthing problems too take a look down by the battery as a lot of the engine loom earths there and corrodes

We did wonder about the throttle pedal, but that generates its own series of errors. As far as I know the aggregate value of the two pedal sensors is combined at the ECU and that forms part of the calculation that may eventually move the butterfly valve; In theory it shouldn't be possibly for the pedal to trigger a fault with one angle position sensor alone as there isn't a direct connection. We tested it anyway, and the values coming back from the pedal seem to be within range.

What usually happens is that the EPC and Traction Control lights will illuminate either as soon as I start the engine, or part way into a journey. This immediately puts it into reduced power mode, and kills the boost. Over the next mile or so it'll get slower until it starts to struggle and hunt. If I stop and turn the ignition off, then turn it on and wait for the basic setting to finish, it'll usually only illuminate the traction control light but will drive fine. The next time I restart it'll run fine with no lights, but may trigger the fault again at some point. The exception is that it'll either hunt, misfire and overfuel really badly on the occasional start, or if the lights don't both go out on the second ignition cycle, it'll misfire and hunt on the third attempt before going back to normal. There's no consistency to when it happens, and we haven't been able to find a situation that'll trigger it. The only correlation was that for two consecutive days a couple of weeks back it lit up the error lights when I returned to the car at lunchtime, and it did exactly that today as well.

It all sounds like an intermittent wiring problem, but we've checked all of the resistances across the cables between the ECU and throttle body, and tugged the cables all over the place with no glitches. We put the patch wire in I mentioned above, and also checked and cleaned the internals on the TB, but as it's happened with two different ones it's probably not that. What gets me is that it happens with no drama, and often before I've even touched any of the controls, so it's not as if we can link it with a physical cause such as vibration or movement. It's as if it occasionally loses the ability to compare or interpret the angle sensor positions, and decides that sensor 2 probably isn't right - not too high or low, but just implausible.

The only issue with swapping parts for test units is that I can never tell how long it's going to take for it to recur. I had about ten days grace this time, and before that it was ditching ever other day. It's a bugger

i think it is more to do with the resistance. can sometimes be caused by earthing problems too take a look down by the battery as a lot of the engine loom earths there and corrodes

We had a look over those as a matter of course, but all seems fine down there. In my experience a major earth issue tends to have wider consequences than a single repeating fault code related to one component. The two angle sensors in the throttle body share an earth direct from the ECU, with a separate one for the motor, so any earth related glitches should affect both of them equally.

well it sounds like your best bet is to try an ecu that has had the immobiliser defeated, you say you dont want to go there but its the next logical and easyiest step i think

By not going there, I was thinking in terms of paying the price for a new one Trying a used but tested one or getting the current one doctored is definitely a possibility.

What I couldn't work out was the prices given by companies on the net selling used but guaranteed ECUs, and how little they were going for compared to new ones... although I did notice many say they won't take them back if they don't work as the car may have damaged them, so that warranty clearly isn't up to much I suppose fitting an ECU with the immobiliser disabled would also invalidate insurance for that period because you'd have lowered the security on your car.

I suppose fitting an ECU with the immobiliser disabled would also invalidate insurance for that period because you'd have lowered the security on your car.

correct, providing they find out, unless you tell them and pay a higher premium then you would be covered