Cold Start Diesel Engine: 101 PS Below 0°C

Hello!

I have a Fabia TDI PD with 25,000 km, and since last winter, I've been experiencing a problem: below 0°C, the engine doesn't start as smoothly and responsively as it does in the summer, even with the glow plugs activated (which should take less than 5°C to activate). The colder it gets, the worse the problem becomes. After the glow plugs activate, the starter motor turns strongly (it's not a battery issue), and it seems like the engine is about to start, but it sputters for 1 to 2 seconds, sometimes dies immediately, or it manages to catch and briefly revs up to around 1,500 rpm, while emitting a thick gray cloud. Then, for the next 10 seconds, it usually runs unevenly and still emits some blue/gray smoke.
The acceleration is noticeably weaker as long as the engine hasn't reached its full operating temperature – it's quite sluggish. Is this normal, or should the electronics compensate for the increased friction/fuel condensation? Of course, I'm not demanding much from the engine when it's cold, but the acceleration is significantly weaker. The glow plugs were replaced as a precaution, but it didn't help. There are also no error codes stored, so the workshop says there's no fault and I'm being told to wait. The starting behavior is particularly pronounced after the vehicle has been idle for several days. I don't use biodiesel.
'In summer, when the outside temperature is above 20°C, a slight, brief vibration can be felt at idle speed, occurring approximately every 10 seconds. However, there is no visible fluctuation in the engine speed according to the tachometer. Could this be related to the 'winter problem'?'

Best regards, and thank you in advance for your replies!

Ralf.

Hi.

It could be due to the engine temperature sensor. If it reports significantly incorrect values below the error threshold, it can disrupt the starting behavior and potentially also the idle behavior.

Is the fuel system okay (filter changed at the correct interval, no air leaks)?

Regarding diesel engines, there are no power problems caused by fuel condensation .

Hello,

Just because the glow plugs have been replaced doesn't necessarily mean they are actually working.
Check if there's voltage at the glow plugs during the preheating process. Overheating the glow plugs by tightening them too much during preheating can cause them to fail quickly.

Best regards, Rainer.

Okay, I also have the 100 hp PD engine in my Polo. In my case, when it's below 0°C, it starts immediately, but it runs roughly for about a second and shakes quite a bit, after which everything is fine. I've also noticed a loss of power, which is probably normal for a cold engine.