[W126 Coupe] rough idle

[Doug Gavin]

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

>>

>

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>

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