What are the probable reason for presence of oil in intake pipe of a turbo fitted diesel engine?

There is always a pipe through which turbo is fed with oil to lubricate the bearing and turbine pipe, if the bearing is worn or the seal defective, oil will be escaping to the intake pipe.

لعدم نظافه الصمامات اذا كان المحرك بحاله جيده اما اذا كان يعمل منذ اكثر من50000 كيلو مثلا فمن الوارد انها شنابر تنظيف الزيت التى تقع على جانبي المكبس

In a closed ventilation type engine, If the piston compression rings   exessively worn out, the blow-by gases passing through would have more unburned oil particles and enter into the inlet manifold.

main cause of this oil pipe is ,to lubricate the main bearing and turbine shaft of the turbo charger assembly.and the reason of oil presence in intake pipe is,,due to the oil seal or main bearing,and turbine may be worn,or brocken.

The seal's in the turbo need to be replaced

In case of turning on and off the engine with full acceleration 

In turning on the machine the turbo charger will run at high speed and the oil flow didn't reach the bearing

In turning off the machine the oil flow will be cut suddenly with high engine speed

Due to the absence of lubrication in this to cases a damage will be occured in the bearing and the oil will be mixed with air

The main cause of the oil vapour in the intake is the design of the breather outlet in the rocker cover.
When the engine is at high RPM the oil that is splashing around the camshaft also gets thrown out of the breather spout.
Some people on the Aussie site have fitted a deflector inside the rocker cover to reduce the amount of oil expelled out through the breather, or you could just fit a catch can.

Defectuosity of the turbo

In light vehicle diesel engine, not only the defectiveness of the turbo, it includes the defective valve seals,oil ring and inlet valve has a gas cutting at landing surface of the valve and valve guide.
if the valve seal and oil ring has a leakage the oil goes to combustion chamber then during the compression stroke the oil pass to a defective inlet valve then it will go to inlet pipe.
In heavy duty diesel engine, it is the same on light vehicle diesel engine.
the additional probable reason of oil in intake pipe is that oil came from the oil bath, because the air pass to the oil bath before coming in the engine.
mostly in power plant design and some in marine diesel engine used this.
if there is oil bath it is normal that we can experience it.

The turbo charger is leaking oil will result in runaway engine.

For diesel engines : The main reason of existing oil in the intake pipe after the turbocharger is the failure around the axes of the turbocharger itself , and its need to offering and installing an erection kit to reparing it .
best regards Jamal Nashouqu