puff of smoke on start up

Hello,
I have a 2005 Jetta Wagon and have just noticed a puff of white smoke on start up. I recently replaced all four glow plugs to get rid of the glow plug codes I was getting. That mission was accomplished. We've had this car for four years and it has 168,000 miles on it. We've replaced the turbo, fuel pump, clutch and glow plugs while we've had the car. Which direction should I be headed in order to figure out the smoke issue? Compression test? Is there a way to test the injectors? Can they be cleaned or rebuilt? The car has no other issues and once started, it runs perfectly. Thanks.

You should have the camshaft looked at, known to wear.

Ugh....I had forgotten about the cam issue with BEW engines. I was going to look into the glow plug circuit by unplugging the coolant sensor and then start it, hoping it was causing the glow plugs to cycle off sooner.

A little puff of smoke is kind of normal for diesels. I'm not familiar with PDs, but I believe the unit injectors sometimes loose seal?

Ok, I just disconnected the coolant sensor and timed the glow plug light on the dash. It was around three seconds before it went off. Reconnected and it went off in about one second. The outside temperature is around 50F and the car is cold. There was a very small puff of white smoke when it fired up, although it was running about two hours prior. Is that enough of a difference to assume the coolant sensor is bad in regards to the glow plug function? If I understand correctly, the sensor has two functions: one is for the glow plug circuit and the other is for operating temperature. The gauge appears to be working fine.

You also might have leaky/worn valve stem seals, but I'd eliminate all other possibilities first because replacing valve stem seals is a PIA.

Cheers,

PH