Bosch pump accelerates by itself

[remy16]

Current problem on my 1995 MK4 transit: it accelerates by itself as soon as it is not in gear.
The pedal/pump cable returns to zero, the oil level remains stable.
The Bosch pump has already been tested by a diesel specialist a little less than 4000 km ago with the same symptoms. Apart from a slightly high idle, operation had returned to normal, to gradually recur since 1500/2000 km
I do not know what to do

[cherniy_chack]

It is difficult to solve a problem with minimal information and via the Internet...
The high pressure fuel pump may be out of order and the injectors may be faulty.
The injectors may also be in good working order, but diesel fuel can enter the engine crankcase through a leaky membrane and evaporate there when the engine heats up, as a result of which fuel vapors will enter the cylinders through the boat's ventilation system and the engine speed at idle will increase. The oil level may then don't change.
First, change the fuel booster pump, which is located on the engine block under the exhaust manifold.
And then you will share the symptoms of the malfunction and, I hope, the collective wisdom will help solve your problem.

[remy16]

Bonjour
...vous voulez parler d'une pompe de gavage ?
Où est elle
Merci

[cherniy_chack]

There may be another reason for the increase in engine speed at idle - wear of the parts of the centrifugal mechanism of the speed controller.
The original pump must be 29 years old, which is a very long time.
But with such wear, the idle speed should change spontaneously or not change at all.
When the plunger pair wears out when the engine and fuel in the tank warm up, the speed decreases as a result of increased leakage in the plunger pair while the viscosity of the fuel decreases when heated.
The only thing that comes to mind is the formation of flammable vapors in the engine crankcase and the increase in engine speed as a result of their entry into the combustion chamber and combustion there.
How can flammable vapors form in the crankcase?
If fuel gets into the oil.
How can fuel get into the oil?
Through a faulty injector or through a faulty booster pump.
In fact, oil vapor also burns well in the combustion chamber of a diesel engine, and the oil itself, which, if the rings and liners are severely worn, can enter the combustion chamber and cause an emergency mode of the diesel engine, which we call “runaway.”
The engine develops high speeds and smokes black smoke.
This usually ends in engine failure.
But you write that the oil level does not change.
Therefore, I exclude working with oil vapors.
What can I advise you - when idling, open the oil filler cap and look at the amount and color of the gases coming out of it. During normal operation, the gases should be colorless and both the exhaust of gases and the intake of air into the neck should be noticeable.
And also, the idle speed will begin to increase; open the oil filler cap and watch the revolutions. When the engine runs on oil vapor, the speed should decrease, because the vapor escapes into the atmosphere.
Good luck!