Dear experts,

I think that finally -thanx to your help- I found the reason of the bad idling. Have a look at the picutres and judge yourself.
The fuel tank seems pretty dirty, I assume that the filter of the fuel pump is not looking much better. Preventively I will change the fule pump (old one 170.000 miles).

What do you guys suggest to buy the whole unit or just the motor unit which should be much cheaper (part number?) and how would you clean the diesel tank?

Thank you for your suggestions.

Best regards
Stevan

Youtube, diy fuel polishing.

Forgot to add pic of the one I made, I cannot take credit as I copied the guy off youtubes design.

12volf copy facet pump
Cheap Racor copy filter
Old copper pipe and some rubber hose

thank you dear Iynall

You can polish the fuel, but that isn't going to get deposits out of the tank.
That will probably best be done by removing the tank & using a solvent to clean it. Easier with the tank off to slosh it around if you can't get at the inside of the tank to wipe it.
Might also want to consider using an inspection camera to see exactly what is inside the tank before taking it off. Available off ebay etc for not a lot to use with your mobile phone. Perhaps someone can recommend a good one, I can't help as I've got a dedicated one.

Might be an idea to thoroughly clean your pump & its filter before buying new parts & see if it makes any difference.
Clutch & brake cleaner aerosols are usually pretty good at blasting things clean.

As for part numbers, put your vehicle details in the post.
Have a look at this link, select your vehicle & you'll see what parts are available & the part numbers.

If you want to see real deposits in a diesel tank then have a look at this:
www.youtube.com/watch?v=7-81v9eUhyk
It's an ally tank so it isn't rust scale/scabs.

dear Ratae,

thank you I will -as you advise- clean the tank with brake cleaner and wipe it out in detail. I ll keep you informed. Best Regards Steven

Dear experts,

finally I changed the low pressure fuel pump and cleaned the gas tank mechanically (see pictures). I have to admit that the car runs much better. Before the pump change I acknowledged rough idling, low accelaration and the rev meter was going up and down.

Now:
- def. better accelaration
- better mileage
- the revs are much more stable now but from time to time (standing uphill) still they go up and down?

What could it be? High fuel pressure pump or maybe the fuel pressure regulator? Diagnosis show no faults.

Thank you for your tips and hints.

Best regards
Steven

Unless there is still some crap in the rest of the system.
At a pinch some decent fuel system cleaner and a good run?