Bosch is good, genuine MB is a 5 year cap. Bosch typically is 3-4 years.

New plugs every year
Cap and rotor every 3-4 years
Wires every 6 years

Don't ever adjust the lambda or the eha, that is a bandaid fix, and you will never get your car to run properly. That 300se should get at least 17mpg, perhaps almost 20 with highway driving. This is the most important indicator whether your m103 is running properly.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

I can only speak of my Bosch plug leads , or spark leads .And the trouble i had with BOSCH .The quality looked good. That was untill i was going to to fit them on to the distributor , and the plugs .You know that our leads need a plug conector puller to remove them, and you hear that snap as they are removed . And on fitting them back on .I did not get this . Looking inside the rubber boot it was just a copper crimp on rubbish inside .That was the reason it never made tha noise to say , yes i am in place; So just take a good look at the new leads before you purchase them .I wont be buying Bosch any more .And they are made in China now. After this i am thinking they cpould have been fake .

All my HT is now MB original aside from Beru leads. I've had them for a few years now with no problems.

As HT is so critical on these cars, I would urge everyone to specify MB original, despite the horrific cost. I know, it's easy to spend your money but experience has taught me that quality counts.

RayH

An item that get over looked is the filter in the area of fuel pump .Also you have a none return valve if its bloked it will restrict fuel pressure.