[W126 Coupe] Stalling/idling issue

[Dick Spellman]

Hi Tony:

If the car appears to have no controlled idle or requires that you 
depress the gas pedal a small amount to start then I'd check your 
throttle position switch (TPS).  This is easily tested by placing  an 
ohm meter across the center and side terminal on the TPS circuit.  You 
can see how this is done by reading 07.3-152 in the MB manual.  I am 
just replacing this same switch on an 86 126 chassis 300SE Euro today.

If on the other hand you have a rough engine at all speeds, I'd check 
the following and replace as needed:
Bosch W9DC or W9DCO)
Bosch rotor
Bosch cap

You say you did the wire set so you should be all set.  The vacuum line 
you refer to on the distributor with the faulty check valve is another 
story.  If you have the early model 380 distributor it may well have two 
vacuum lines.  One for vacuum advance and the other for vacuum retard.  
The check valve(s) must be working for these two vacuum functions to 
work.  I'd replace with the original MB specified valve and then check 
the lines and diaphragms using a Mighty Vac.

If after all of the above tests and repairs you still have problems at 
least you will have ruled out most of the common electric issues.  I'd 
then move on to testing the fuel system pressures and injection.

Worse case Tony now that I sit here realizing we know each other, is 
drop by my house and I'll take a look for you anytime this am.

Dick
508-641-8477

Tony Damar wrote:

> Hi all,
>  
> My 380SE has recently started acting up with a rough idle.  It will 
> start and stay running as long as it's in P or N.  Once under load (in 
> gear or A/C on) the rpm's will drop to around 200 - 400 rpm and the 
> car will sputter and die.  It will start up again immediately.  I 
> suspected the plug wires as some of the insulation had been worn off 
> the boots.  We had a hard rain the day it stalled on me several times 
> this past weekend.  I replaced the plug wires.  While doing so, I 
> noticed that one of the vacuum hoses was loose.  It had broken 
> off (what looks to be) a check valve.  I had picked up one at Autozone 
> (non-MB) to see if it would help.  It's not a perfect fit, but it 
> seemed to make a difference that night test driving around and the 
> next morning on the way to work.  During the afternoon, it did not 
> want to run while in gear.  
>  
> My question is what is on the side of the distributor cap that leads 
> to a vacuum line.  It is silver looking and runs to what looks to a 
> check valve (the broken one mentioned above).  Also, could this be 
> fixed by doing what Eric Harder did in removing his air idle valve and 
> blocking it off?
>  
> My car has 302K miles on the original engine (newer camshafts).  I had 
> some issues similar to this about 50K miles ago and replaced the 
> following: Ignition computer, idle control relay,  fuel injectors and 
> seals, ignition tumbler, spark plugs and a couple other things that I 
> don't remember off the top of my head.
>  
> Next on my list is the distributor cap and rotor and new plugs.
>  
> Any and all help is greatly appreciated in advance!
>  
> Tony
>
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