The idle being not good I decided to replace the whole set of sparks cables, but on cruising speed no misfire at all, I would say perfect.
The old cable are the original ones, Bosch make, they are 18 years old.
I bought a complete set. The dealer sold a full set from Beru with the following references.

Copper cable bestel-Nr
1 M107-A 0 300 811 382
2 M107-A 0 300 811 382
3 M107-B 0 300 811 383
4 M107-C 0 300 811 384
5 M107-D 0 300 811 385
6 M107-D 0 300 811 385
7 M106-B 0 300 811 378

Some pairs are of the same length N°1 and N° 2. The new cable for spark N°1 is 10cm longer than the original.
The same length for N° 4 and N°5.

After I put them on the engine the idle is worse than before.
I suspect I have not been sold the correct set of cables.

Can some body help to check if I have been delivered the right cables.

Should they be of different lenght?

Can an incorrect length bring incorrect timing of ignition and therefore bad idling?

In advance many thanks for your help.

__________________
Keep us posted especially if your problem is solved
Present cars:
My car: E-class 420CDI, 2008, W211, V8, 180 000km

Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km

Son's one: GLK class 220CDI, 2009, W204

Sold E class 260E, W124, 1988 beloved car sold after 489 000 kilometres of reliable services (engine M103, clutch and 5 speed manual gear box all original).

E-class, W210 320CDI, 2000[/B], 225 000km, Sold

First of all the original MB wires are not Bosch they are Beru. The length of the wire doesn't matter except cosmetically and to keep the wires off hot manifolds. The spark travels the speed of light and length has no bearing on timing. Most dealers sell kits made up by Bosch or Beru. MB doesn't sell a kit, they sell wires individually.

We almost never replace complete sets of wires as defective wires and cable ends are an easy diagnostic to a professional. We build our own wires from components as necessary. If damaged by fire or setting on manifolds or too many careless hands we will then replace a set.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thank you stevebfl,
sorry to come so late, thank you for the useful info.
From visual inspection the old cables were not damage at all, and I could have saved some money. But I thought it was a good idea to chage them after 18 years. The new ones do not bring better ignition.

__________________
Keep us posted especially if your problem is solved
Present cars:
My car: E-class 420CDI, 2008, W211, V8, 180 000km

Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km

Son's one: GLK class 220CDI, 2009, W204

Sold E class 260E, W124, 1988 beloved car sold after 489 000 kilometres of reliable services (engine M103, clutch and 5 speed manual gear box all original).

E-class, W210 320CDI, 2000[/B], 225 000km, Sold