F8Q cylinder lid

Hello friends! I have a 1.9 diesel Express with the F8Q engine. The thing is, a month ago I was coming back from a trip and the timing belt stripped; several teeth were lost because it had a leak and got soaked in oil. The cylinder head was removed, had to be rebuilt, inspected, and all the valves, guides, and valve face were replaced, and a hydraulic test was performed.
Since it was reinstalled, I've had a problem that's been driving me crazy. When it's cold, it starts misfiring, like it's only running on three cylinders, and emits white smoke. This lasts for about a minute, then it stabilizes and doesn't misfire anymore. When I'm driving on the highway at over 100 km/h, it tends to have a slight jerking or sputtering issue. Thinking it might be the injection pump, I took it to a fuel injection specialist, and he says it's fine and that the problem is with the cylinder head (he also finds it a strange problem). When he removed the air intake hose, there was oil in the intake manifold.
I'm going to remove the cover again and have it checked again, but I have some doubts about the oil found in the intake.
I look forward to your comments.
Regards

Did you apply the correct torque when assembling it? Check for cracks, as that's a common sign of water leaks. Good luck, and keep me updated on what you find.

Hi JAL!! And thanks for replying!!
I applied the torque exactly as the adjustment manual specifies, in degrees. I don't have any problems with the coolant; in fact, I checked if it overheats and it doesn't. It stays between 80° and 85° at any speed.
The engine only has 45,000 km on it. I had it sleeved to standard specifications and it never gave me any problems until the timing belt broke. Now, it only misfires when cold (it starts on 3 cylinders for about a minute, during which it emits a lot of white smoke). When you're going over 100 km/h, you can notice a slight misfire every now and then. Other than that, you don't even notice it. What's really bothering me is the appearance of oil in the intake manifold (the engine isn't smoking, and the exhaust isn't venting).
Could the cylinder head be cracked? And why does it start misfiring when cold, emit white smoke for a moment, and then stabilize and run perfectly?

Thanks and regards.

Check the lid carefully for any cracks; white smoke is a sign of water entering the cylinder. Good luck, and let me know if anything changes.

Dear friend, the misfire and excessive white smoke when starting your engine could be due to the following:
faulty injectors. They lose pressure overnight, and the excess fuel in the cylinders produces the smoke. The misfire persists until the injectors regain the operating pressure they need to maintain overnight.
If the oil in the intake manifold is just that—oil—without leaks or turbocharger issues, then that moisture is normal. However, if there are leaks and the turbocharger is present, the problem could be the turbocharger.
I would like more information about your engine since I don't know its serial numbers or what vehicle it's in. I hope this helps. Best regards.