Slightly odd cold start problem

[mrman17]

Hi all,

I need to pick your brains (I have done a search, but not seen anything like this one). This is with a MK3 GTi, AGG engine.

So far it has mostly happened (intermittently) on the coldest mornings - while cranking it will not start. You keep trying and on the second or third attempt as you release the key from cranking, it will catch. Afterwords it starts fine.

The other morning, it would not start at all, but coming back later in the day it did.

I have noticed that the rev counter does not come off its rest when cranking (when it doesn't start that is - it should usually go up to around 200rpm or so), which suggests it's an electrical problem in the LT circuit somewhere.

At the moment the only thing that comes to mind is the ignition switch. However, it does seem odd this only seems to happen when it's "cold". The ECU relay has already been replaced.

Any thoughts appreciated.

Added: Meant to say that there's no fault codes.

[mrman17]

The only other ideas I have at the moment are:

1) Ignition switch
2) Crank/engine speed sensor
3) Immobiliser
4) The earth cable connections

I'd have thought 2 would have shown up in the fault codes?
 

[javalin]

Coolant temperature sensor?

If it cranks at a decent rate, I would discount your idea's.

James

[mrman17]

I thought I would update this, in case anyone else had/has the same problem.

I had been thinking when cranking over, it seemed a little "lazy". Because of that and as I've had it 7 years now I thought it was worth chucking a new battery on it just before the latest spell of cold weather.

It's been fine since, even with today's snow, etc.

I suspect, although it was cranking over "OK", the battery voltage dropped enough where the spark was too weak, or not present, so would not start. Releasing the key took the load off the battery and allowed a good enough spark, hence would "catch" and run.

Hopefully it is just that, a knackered battery, and not masking any other problems (like corroded connections, not had chance to check them), but it is otherwise fine at the moment.

[javalin]

good news then.