[W126 Coupe] rough idle

[Doug Gavin]

Jonathan wrote:

> Doug Gavin wrote:

>> Gerry Van Zandt wrote:

>>> Reman fuel heads (fuel distributors) in general are, I hate to say 

>>> it, problematic -- even the rebuilds that Bosch themselves do. Your 

>>> best solution -- and I know it is not cheap -- is to get a factory 

>>> new unit from MB. Last time I checked they were over $2K from MB, 

>>> but at least they have a warranty on them, and you know what you are 

>>> getting.

>>>

>>> This definitely sounds to me like a fuel distributor or related 

>>> issue. My second guess is a vacuum leak -- similar deduction to you. 

>>> Have you thoroughly checked out the ENTIRE vacuum system for leaks?

>>>

>>> Cheers,

>>> Gerry

>>>

>>>

>>>

>>>

>>>

>>> On Aug 9, 2007, at 4:28 PM, mbcoupes-request at mbcoupes.com wrote:

>>>

>>>> Message: 8

>>>> Date: Thu, 9 Aug 2007 11:43:45 -0700

>>>> From: "Tim Graney" <graneyt at americancylinderhead.com>

>>>> Subject: Re: [W126 Coupe] rough idle

>>>> To: "'Mercedes Coupes Mailing Lists'" <mbcoupes at mbcoupes.com>

>>>> Message-ID: <000001c7dab5$37d06b10$7901a8c0 at timpc>

>>>> Content-Type: text/plain; charset="us-ascii"

>>>>

>>>> I bought the FD from German Star...? I did replace all the rubber

>>>> gaskets in the plenum. vacuum stays nice and steady but does hiccup

>>>> every once in a while. I have looked till the cows come home for any

>>>> vacuum leaks. where does one get the right spark plugs...these are 

>>>> Bosch

>>>> plugs. what gap should they be? Thanks again

>>>>

>>>

>>> The MB Coupes Website!

>>> W126 SEC Mailing List

>>> Postings remain property of MB Coupes, L.L.C.

>>>

>> I priced a FD at CarQuest Auto Parts. New Bosch they would sell for 

>> $1700 although the MSRP was $1950.  Gee, thanks! Ouch.

>>

>> Just my two cents. I had a slightly rough idle, in my '90 SEC not 

>> quite a skip but an annoyance more than anything. My indy MB mechanic 

>> replaced 3 injectors and the car ran as smooth as silk for about 3 

>> weeks and the same mild roughness returned. I guess we could replace 

>> all of the injectors but at the cost of injectors and labor, I'll 

>> live with the slight roughness. He told me that he sees this  often 

>> in the 560s and it's difficult to solve and that he knows we might 

>> have to mortgage the house to get it to my satisfaction.

>>

>> Prior to having the injectors changed. (They were the original with 

>> 78K miles) I stopped at Star Motor Cars in Houston and got to talk to 

>> a mechanic that has been there for 18 years and has worked on many 

>> 560s. He told me that condition was very common and he  had addressed 

>> this more times than he could remember. His diagnostics was that it 

>> is the EGR tubes within the engine (my technical term may be off , 

>> bad memory, but some will know the proper term) There is one on each 

>> side of the engine internally.  He went to his tool box and pulled 

>> out a a drill bit about 15 " long X 5/16 " and said this is what I 

>> use this for. He went on to tell me that the carbon build up 

>> restricts the passages of these tubes and causes the roughness. The 

>> most bizarre thing he told me was this was consistent in the 560s and 

>> it would begin  at just over 60,000 miles.  His recommendation was to 

>> get used to it like everyone else did until I had the heads done then 

>> go ahead an have them drilled out. My comment to him was was that 

>> these folks in the late '80s and early '90s  paid around $90K for 

>> these cars and tolerated this? He just shrugged and said, yup. Oh well.

>>

>> Doug

>> The MB Coupes Website!

>> W126 SEC Mailing List

>> Postings remain property of MB Coupes, L.L.C.

>>

> Interesting...I block off the EGR ports on 560's  (as they are from 

> the factory in ECE Euro trim) when I do the heads and they idle 

> beautifully.  Many times when I go in to do said heads the ports are 

> utterly clogged with carbon thus it's not as though much is changing.

>

> I find that hard to understand, I don't tolerate it, and granted it 

> can be frustrating to track down but you Can get these cars to idle 

> beautifully should you really want too.

>

> Jonathan

>

>

Boy do I agree with Jonathan and as I said I can't imagine buying one of 
these Coupes and after 4 years or so at 60K miles have to put up with a 
rough idle. I like things to work correctly and this slight idle 
roughness is annoying but I have my limits to cost vs tolerance at the 
moment. Sooner or later I'll pony up the bucks to make it right and all 
will be at peace.


Doug