T4 ACV engine doesn't sound right when cold

Hello. I have a 1996 T4 with problems when it's cold. The water temperature is around 30 degrees Celsius. It smokes blue, the exhaust smells very strong, and it doesn't accelerate between 1100 and 1600 RPM, even though I'm pressing the gas pedal. When the accelerator pedal is more than 45% pressed, the RPM jumps to 3800. All parameters are within the normal range. I've already replaced: the EGR valve, injectors, and the temperature sensor, but nothing has changed. I've also checked the compression, and it's fine. What could it be? Does anyone have any ideas?

Best regards,
Bernd

Have you checked the fuel system for air leaks?
The fuel pump only kicks in when the fuel temperature reaches 30 degrees Celsius.
Only then can any potential air bubbles escape back into the return flow.
That would, for me at least, be the only explanation for this significant lack of performance in cold conditions.

The fuel system is free of air bubbles, with only a few small bubbles occasionally appearing in the fuel hose. The engine has incredible power. On the first ride, I thought it had 150 horsepower.

The fuel system is free of air bubbles, except for a few small bubbles occasionally appearing in the fuel hose. The engine has incredible power; on the first ride, I thought it had 150 horsepower.
Above a water temperature of 40 degrees Celsius, everything works perfectly again, and the excessive smoking disappears.

Blue smoke when the engine is cold suggests a problem with the fuel injection system. Have you checked the fuel injection start-up? Has a timing belt replacement been done recently? If not, a worn-out timing belt can alter the valve timing, which has exactly that effect!

Timing belt replaced. Timing is 100% accurate.

Again: Has the injection start been checked with VAG-Com?

Injection start is correct, verified with a Gutmann tester.

What I forgot to mention is that a new cylinder head was installed 30,000 km ago due to a timing belt failure. Could it be that the engine block or a connecting rod is defective? The compression is the same in all cylinders.

How was the performance and was there any blue smoke after installing the new cylinder head? Or did you recently replace the timing belt again? Did you install the correct cylinder head gasket with the same number of holes as the old one? By the way, did you only read the error codes, or did you check the injection timing in its basic setting? Unfortunately, I'm not familiar with the Gutmann test.

The engine was running at full power. With the new head, the timing belt was also replaced. The head gasket has the same number of holes as the previous one. Then the issue with the blue smoke started. The error memory only showed a temperature sensor, which I replaced. All parameters are okay. The fuel injection also starts correctly.

Hmm.. Was die NW (Nockenwelle) betrifft, wurde sie mit einem Lineal und einer OT-Markierung am Schwungrad (nicht am Riemenscheiben) wirklich zu 100 % auf OT (Obere Totpunkt) ausgerichtet? I know, it's really hard to get a good look .
Did the pistons have any cracks besides valve marks? How is the oil consumption? A possible cause in cold conditions is a sticking fuel injector, which can be observed during the start-up phase. If the injector is too slow to open, it can lead to blue smoke and a lack of power.
For safety: Are all 5 glow plugs working correctly? Is there voltage when preheating? (Can the Würth tester perform an actuator test?) Otherwise, try this: Disconnect the temperature sensor connector; this will simulate a temperature of -48°C, which should result in very early fuel injection and afterglow. Try running the engine once without the LD (Lean Definer) hose. Dan berichten Toitoi.