Golf GTI 18T AUM poor cold starting

[atomicgolf]

I have a golf mk4 2001 with an AUM engine and it's a bugger to start from cold. usually 4-5 goes @ 25 seconds + cranking. when you stop cranking I can hear a 'small pop' from the exhaust like it's just fired once but then after some cranking it will burst into life.

When warm it starts instantly. Occasionally it will start instantly when cold but not very often.

My brother is a mechanic and we plugged a snap on tool in and found the following codes
17748 Camshaft position sensor p1340
17704 error in mapped cooling system.
All the live values like water temp and intake temp look OK.

So I have done the following,
replaced the timing belt (which was due anyway), water pump, tensioner and guide
verified the engine, valve and chain timing all are spot on
replaced the water temp sender and thermostat
no the engine management light comes on now and again with just the 17748 cam sensor fault.

I also changed the oil, oil filter and air filter, cleaned the throttle body but the issue persits. It also idles at 1500 rpm for the first 2 mins before settling to a normal idle. it also drives spot on hot or cold. No miss fires or lumpyness.

Has anyone else encountered this issue? Or have any pointers?

[atomicgolf]

Just a quick update for anyone interested, This morning before I attempted to start the car I turned the ignition on and off about 5 times with a 5-10 sec pause so I could hear the fuel pump click on for a few seconds each time. As soon as I turned it over it fired straight up and was as smooth as I'd expect. I am going to change the fuel filter and see if that helps. The engine light came on again whilst driving and I'm still getting 17748 Camshaft position sensor p1340 so I may also change the crank sensor as the camshaft sensor has already been replaced by the previous owner last year and still the error persists.

[atomicgolf]

Last update as the car is now sorted. The VAG-COM logged three different cam sensor codes and it turns out the fault was a camshaft position sensor. I fitted it this morning and the car is starting on the button and has a lot more low down torque than it had. I have cleared the fault codes amd in 20 miles of driving and lots of starts it's still spot on. no new faults showing.

Great stuff. I also removed all the main sensor connectors and used a service spray to clean them and refitted.

Well chuffed with the outcome