Intermittent starting problem

[phil mcglassup]

Hi All,

For a while my Audi A4 B6 1.9 Tdi (2003 with 167k miles) has had an intermittent starting problem. When starting from cold it will start for a split second, the revs reach between 600 and 1200 rpm before stalling. Usually it needs many attempts before it will 'catch' and start, although as the revs begin to rise it runs rough but then runs and ticks over perfectly and will start first time when warm. Sometimes it starts from cold with no issues. There is no engine management light on nor any other warning lights. At the time of typing, it won't start at all !!

I've tried a few things to no avail , i.e. using the spare key, disconnecting the battery for twenty minutes and banging on the ECU (poor relay connection) as these are the things that have been suggested when doing searches. There is one suggestion that it could be the camshaft position sensor as apparently they are prone to failing, but it is a massive job if it isn't the fault!! I changed the cam belt and water pump only 2000 miles ago.

Apart from taking it to a garage, any other suggestions ? I certainly can't compain about the car as it's been very reliable and cheap to run so far !!
Any help appreciated.

 

[Mike B]

A diagnostics check should help but my guess would be the coolant temp sensor is faulty.

 

[phil mcglassup]

Thanks for the reply.
Can the coolant temperature sensor be faulty even when the temperature gauge is showing an accurate temperature ?

 

[pauldazzle]

Coolant temp sensor would be my first suspect as it's a common failure on VAG cars from that era.
N.B. Coolant temp sensor has 2 seperate outputs i.e. 1 to the gauge & the other to the ECU.

 

[Mike B]

Should be easy to replace CTS but use a genuine one

 

[pauldazzle]

As above genuine CTS only, buy cheap, buy twice.

 

[phil mcglassup]

Could it be that the the output to the ECU has failed ? And the temp gauge ouput is okay?

Is there a temporary bodge I can do to get it started in the meantime as I doubt Audi will have one in stock and I need the car for work.

Thanks for the replies

 

[pauldazzle]

Precisely, it's common for one output to fail.
You should be able to get one from any VAG Dealer or your local TPS.

 

[phil mcglassup]

Hi All, thanks for all the replies. Here's an update for reference.
Before I invested in any replacement components I took it to a local garage for them to assess.
They found that the glow plugs were not working, but replacing them did not cure the starting problem so they looked at the camshaft position sensor which had a piece of crap stuck to it!! Once cleaned, it struck up perfectly and it has started first time every time since I got the car back, so I'm hoping they've cured it and the current good starting is not by chance!!

 

[Mike B]

Good news but wonder what it was and where it came from.Recent warm weather probably helped with no plugs working

 

[phil mcglassup]

Could be...yet I never had any starting problems prior to this. I've no idea where it came from as it was nothing I did !!
It's still starting okay and I can tell it's better, as before when it did start it used to run rough as the revs rose between approx 800 to 1200 rpm, but it's okay now

Thanks all.

 

[Mike B]

Was it inside or outside?Sounds like it was outside fouling the connector.

 

[phil mcglassup]

To be honest I think he implied it was on the inside !! There again I have no idea where it fits etc but he said he removed it, cleaned it, then put it back.

HTH

 

[Mike B]

That seems unusual hope it doesn't happen again.Perhaps it needs it needs an oil change.Hope its not on longlife servicing.Wonder why the glow plugs failed.Mine still good after 15 years

 

[phil mcglassup]

Seems odd. Oil has just been changed. As long as it starts and runs okay...I'm happy
I haven't spent much on it since I bought it considering the miles I do in it !!