I have very rough starting, often hard to start, on a 1989 300E. I have just replaced the injectors and seals. Shop says I have rust, varnish, or other debris washing through the fuel system, clogging tiny orifices, etc. Their mechanic showed me rust or something in the fuel being bled from the fuel distributor. After this was repeated on all of the nipples, the engine was idling better.
Once the car is started and the obstruction clears, the roughness largely disappears, but idle is still uneven.
I notice no rust or other material when bleeding fuel at the nipples on the fuel distributor, so the shop says try using commercial fuel line cleaners and if this does not do it in three tanks or so, the fuel distributor will need replacing. I have used STP Fuel Treatment and Slick 50 Fuel Treatment, but still have the very hard starting and rough running until whatever is clogging an orifice is dislodged. (This is the view I have gained from what seems to be a good shop)
If I really have nothing but hard starting due to debris in the fuel line I can live with this until I can afford another expensive repair, and use some more fuel line cleaners meanwhile. Question is, can I replace the fuel distributor myself? I have the usual array of combination wrenches 4-24mm, 1/4 and 3/8 sockets, allen sockets and basic hand tools. Am I properly equipped? After replacing the injectors, this looks easy enough. Am I missing something, believing this looks like a simple remove and replace job? Any advice, magic incantations, etc. would be sincerely appreciated, since it looks like a savings of $300 or so.
At the same time, can you recommend an alternative remedy, a different diagnosis, or even your favorite fuel line cleaner?

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If you are having rough starts, you might want to drain the tank. I have seen fuel tanks that have water in them cause this.
After that, if you still have the rough starts, you may want to HAVE the fuel dist. replaced. I do have reasons for having it done instead of doing it yourself. What about warranty? If it leaks, are you going to warranty it? You have to get the lambda reset anyway. Save yourself the headache and let a shop do and give them the worry.
Good luck,

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

On the topic of fuel system additives: I have had excellent experience with a product called "BG44K." I think it is somewhat hard to find but I have always been able to find it at my Toyota dealer (I also own a Toyota). It is somewhat expensive, I pay about $20.00 for an 11 oz. can but I have seen substantial performance improvements after using it.

I agree with Benzmac. Have the distributor head done at a shop because as he said especially concerning lambda adjustment. If you have a meter, then fine, but I'd have it done by someone who's done it before. If you do decide to jump into it yourself, you can e-mail me for the specifics. Oh, you might also want to try the Red Line fuel cleaner product. I have only seen it on their website, and don't have any past experience with it but I can say their other products are wonderful. Check PartsShop to see if they have it.


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Rgds,
Aaron Greenberg
MB technician
'67 250SE Cabriolet
'77 450SL
'79 6.9
'79 6.9
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8

We do carry all of those cleaners in the partshop! Look at the top of the page and click on the ad.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM