[W126 Coupe] HELP! Car Salling!!!!!

[Dick Spellman]

David:

When you say you cleaned under the throttle plate, you were referring to 
the air volume meter???The plate just under the air cleaner?  The 
throttle body is at the very bottom of that entire assembly.  It's the 
first item bolted to the intake manifold.  If that throttle plate does 
not fully close the TPS will see an 'open' which will mean that the idle 
will sit lower than normal.  The idle may stumble a bit where it's lower 
than prescribed.  If you put your foot on the accelerator while in park 
and bring the rpms to say 650 (normal idle) is the engine nice and 
steady?  If it is, you need to test the TPS and I think you'll find it's 
simply a carbon build-up on the throttle body preventing the plate from 
closing fully and the TPS from reading 'closed'.

To test for a vacuum leak, remove the air cleaner assembly, take a spray 
bottle filled with water and work the spray a bit at a time all around 
the intake manifold and vacuum lines/valves along the driver's fender.  
If you hear/feel the stumble worsen or get better concentrate on that 
one area to route out the leak.  I do not recommend spraying carb 
cleaner or solvent because it eats at the rubber fitments over time.  
Another way is to take a propane torch (not lit) and open the valve and 
work around the intake to see if the idle smooths out at any point.  
Test each of the injector seals or fuel rails in this manner as well.  
Stay away from the hot exhaust and spark plug wires where you can.   
Jonathan pointed out to me some time back the frequent failure of the 
purge hose that goes into the driver's fender.   That's an easy check, 
just pull the fat short rubber hose and see to see if it has a dry loose 
fit.  Another vacuum leak I found was the headlamp elevation vacuum 
circuit.  On one MB it was the dash dial and on another the vac line to 
the passenger headlamp.  Easy enough to pull the lines at the dash just 
behind the elevation dial and close them off to see if that makes a 
difference.  A Mighty Vac does help if you can get your hands on one for 
some of the line tests like the headlamp vac circuit.

The air slider hoses can dry out and leak.  Keep at it and you'll find 
the problem(s).

 David Fatovic wrote:

>It sits towards the middle, closer to the left as
>looking at it.  
>
>I took my lunch break today and pulled the Idle
>Control Valve and cleaned the shit out of it.  Almost
>litteraly.  I also cleaned under the throttle plate. 
>Now on my way back to the office the car did not stall
>on me once, even when warm.  However, idle did get
>close to it.  The idle did drop below 500rpm a couple
>times at a light.  It was also rough.
>
>So now the question is.  I assume I have a vacuum leak
>somewhere that is messing with the idle a bit.  It is
>also making it rough.  What is the easiest way to find
>a vacuum leak?  I don't have any vacuum test tools. 
>Where are the usual leaks found?  
>
>David
>
>
>--- "Shayegan, Richard" <rishayegan at davidson.edu>
>wrote:
>
>  
>
>>With the car stopped, engine running, in D, where is
>>your economy gauge? Anything other than pegged at
>>the best fuel mileage side (i.e. the non-red side,
>>IIRC the left side) means a vacuum leak.
>>Richard
>>
>>________________________________
>>
>>From: mbcoupes-bounces at mbcoupes.com on behalf of
>>David Fatovic
>>Sent: Tue 6/6/2006 1:36 PM
>>To: Mercedes Coupes Mailing Lists
>>Subject: Re: [W126 Coupe] HELP! Car Salling!!!!!
>>
>>
>>
>>Would a vacuum issue also cause some sluggishness
>>going from a standstill to the first part of
>>accelleration?
>>
>>David
>>
>>--- Dick Spellman <spell.yy at verizon.net> wrote:
>>
>>    
>>
>>>Hi David;
>>>
>>>Glad to hear you found some improvement on the
>>>      
>>>
>>fuel
>>    
>>
>>>filter change.  Any
>>>way you can test fuel pressures on the system to
>>>rule out the pump,
>>>regulator, etc?
>>>
>>>As for the unstable idle...You may well have
>>>      
>>>
>>several
>>    
>>
>>>gremlins occurring
>>>at once.  It should be relatively easy to test the
>>>throttle position
>>>sensor (TPS) using a VOHM meter.  If the idle
>>>position is not showing
>>>'closed' while the engine is at idle, then you
>>>      
>>>
>>could
>>    
>>
>>>have a carbon
>>>build-up on the throttle body that needs to be
>>>cleaned or the TPS itself
>>>may have failed.
>>>
>>>If the TPS shows open when it should show closed,
>>>just jumper the two
>>>pins on the harness to fake the 'at idle' position
>>>to see if this
>>>improves the stability of the rpms at idle.  The
>>>      
>>>
>>TPS
>>    
>>
>>>is 3 pins total. A
>>>center pin which is 'common' and a pin to either
>>>side that reflect 'wide
>>>open throttle' (WOT) or At Idle.  Be sure you know
>>>which is which as you
>>>proceed with the test.  Then at least you will
>>>      
>>>
>>know
>>    
>>
>>>what to repair
>>>before going further.  There are a number of other
>>>things that could
>>>cause that erratic idle as well but, this is one
>>>that's easy to check
>>>and rule in or out in making the repairs.
>>>
>>>Dick
>>>
>>>David Fatovic wrote:
>>>
>>>      
>>>
>>>>do you remember where you found the computer and
>>>>wiring harness. I will want to check that out as
>>>>        
>>>>
>>>well
>>>      
>>>
>>>>I changed the fuel filter tonight. it did make
>>>>        
>>>>
>>some
>>    
>>
>>>>difference. here is what I found while driving it
>>>>tonight. it goes well while driving, but when you
>>>>        
>>>>
>>>stop
>>>      
>>>
>>>>it doesnt hold idle very well or at all. that is
>>>>        
>>>>
>>>when
>>>      
>>>
>>>>it will stall. it tries to idle around 480-500
>>>>        
>>>>
>>rpm.
>>    
>>
>>>I
>>>      
>>>
>>>>believe that is too low to keep vacuum pressure.
>>>>        
>>>>
>>>what
>>>      
>>>
>>>>could cause this? I did replace the over voltage
>>>>protection relay.
>>>>
>>>>any ideas now? what should I look at to adjust
>>>>        
>>>>
>>the
>>    
>>
>>>>idle?
>>>>
>>>>thanks,
>>>>
>>>>David
>>>>--- mbcoupes-bounces at mbcoupes.com
>>>><igatenby at optushome.com.au> wrote:
>>>>
>>>>
>>>>        
>>>>
>>>>>-----Original Message-----
>>>>>From: mbcoupes-bounces at mbcoupes.com
>>>>>  
>>>>>
>>>>>          
>>>>>
>>>>[mailto:mbcoupes-bounces at mbcoupes.com] I
>>>>
>>>>
>>>>        
>>>>
>>>>>had the same problem - swapped lots of parts
>>>>>          
>>>>>
>>>between
>>>      
>>>
>>>>>  
>>>>>
>>>>>          
>>>>>
>>>>my 500SEC (which had
>>>>
>>>>
>>>>        
>>>>
>>>>>the problem) and my wife's 500SE.  In the end
>>>>>          
>>>>>
>>>(after
>>>      
>>>
>>>>>  
>>>>>
>>>>>          
>>>>>
>>>>months of chasing the
>>>>
>>>>
>>>>        
>>>>
>>>>>problem) it turned out to be that small wiring
>>>>>  
>>>>>
>>>>>          
>>>>>
>>>>harness that attaches to the
>>>>
>>>>
>>>>        
>>>>
>>>>>ignition computer - it had a wire that was
>>>>>          
>>>>>
>>broken
>>    
>>
>>>>>  
>>>>>
>>>>>          
>>>>>
>>>>inside the insulation. 
>>>>
>>>>
>>>>        
>>>>
>>>>>$15 at the wreckers' - problem solved.
>>>>>
>>>>>Ian
>>>>>
>>>>>The MB Coupes Website!
>>>>>W126 SEC Mailing List
>>>>>Postings remain property of MB Coupes, L.L.C.
>>>>>  
>>>>>
>>>>>          
>>>>>
>>>>The MB Coupes Website!
>>>>W126 SEC Mailing List
>>>>Postings remain property of MB Coupes, L.L.C.
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>The MB Coupes Website!
>>>W126 SEC Mailing List
>>>Postings remain property of MB Coupes, L.L.C.
>>>
>>>      
>>>
>>The MB Coupes Website!
>>W126 SEC Mailing List
>>Postings remain property of MB Coupes, L.L.C.
>>
>>
>>    
>>
>>>The MB Coupes Website!
>>>      
>>>
>>W126 SEC Mailing List
>>Postings remain property of MB Coupes, L.L.C.
>>    
>>
>
>The MB Coupes Website!
>W126 SEC Mailing List
>Postings remain property of MB Coupes, L.L.C.
>
>  
>