A couple of weeks ago my 2002 Octavia mk1 was unable to start. It cranks normally, no dash lights or engine fault codes, no weird sounds. It starts normally most times but about once every 20-30 times it does this. Tried both keys with no effect so I don't feel like it's the immobilizer. Temporary fix seems to be locking the car, letting it settle for about five minutes (as if to completely shut down the ECU) and then it starts fine. Battery is almost brand new and terminals connected properly. Has anyone had this before? Any ideas on what to check?

What engine does your car have?

 

On my old mk I Octavia 1.4 petrol you always heard the fuel pump whirring as you unlocked/ opened the door - could this pump be on the way out? 

 

You mention that the battery is brand new - it's also worth re checking battery cables as they will have been disturbed - not just at the battery end but also where they terminate (eg body earth).

Mine's got the 1.6 102ps petrol engine, BFQ I believe is the code. You can hear the fuel pump work when turning the key to its first position.

 

As for the battery, it has been almost a year since I changed it, while the problem first appeared much more recently.

Still I will check any visible wiring and earth cables again focusing on the part immediately after the battery, maybe something has come loose.

Thanks for the suggestion, will come back with an update if I find anything.

Any codes logged? Crankshaft sensor could be a possibility but diagnosis by substitution can get expensive.

 

No codes, I have an OBD2 scanner and it found nothing when I checked. I also connected it when it had trouble starting and it read nothing.

Can you check first principles when it's not starting. Pull a plug lead off and attach to a spark plug(spare?) and clamp against a metal surface on the engine - does it spark when turning over?

When not starting after turning over for a while can you smell petrol at the exhaust pipe - or on an extracted plug?

 

I think this engine also has a wasted spark coil pack that is known for partially failing and are cheapish and quite easy to change - doesn't always trigger a code.

Also the previously mentioned crank sensor - although I would have though that would throw a code.