[W126 Coupe] High Idle issues

[Dan Gardner]

High idle issues seem to be quite common this is a summary of my limited 
experiance.

    All hose connections around the idle air valve had been
sealed using Loctite No 3 Aviation flexible sealing compound as a test
before buying new hoses,all male parts deburred and polished and then 
independantly vacumm tested using a "Mityvac"
.
Air idle valve cleaned with carb cleaner and lubricated with WD40.
    With the engine running and the Air idle valve electrical connection
removed the idle climbed to 1500rpm.
    When starting with engine hot it used to climb to 1000rpm then settle to
650rpm now it is from 1500 to 1100,had tried another idle computer with no
noticable difference.Also a substitute Air idle valve
    When cold the idle creeps from 750 to 1100 as the engine warms up.All
this seems to have happened since I cleaned the valve.(would the build up of 
carbom restrict flow?)

I have been running my SEC with the 45deg plastic bypass tube removed and 
the holes
plugged this has brought the idle down to an acceptable 750 RPM.(from
1100RPM)

    I could not find a vacuum leak anywhere,(as neither could my German 
mechanic)resistance was to spec.(as per CD
ROM)
      At idle the volts while connected are 4.7 cold
decreaseing to 4.1 warm .I am sure you guys said that 3 volts was the norm
which in theory(4.1) should make the engine idle slower than normal.

    What is strange is that most cars I have driven including my 450SL fast 
idle when cold @1000 RPM and depending on ambiant temperature drops down to 
say 650 RPM.But my SEC always climbs to 1000RPM hot or cold for say 10 
seconds and if cold is "lumpy"@ 600RPM then gradually climbs to 800RPM when 
warm.(in neutral)So if one was to fit an airflow restrictor in the air idle 
valve to control the warm idle,when cold it would be "super lumpy".Ideally 
what should happen is that when the corect operating temperature is reached 
a sensor should send and extra 1 to 2 volts to the air idle valve to lower 
the idle.Question is why isnt the idle speed computer doing just that?as my 
German mechanic tells me there is not a fast idle in the true sense of the 
word.

    Its a tough nut to crack!!!!!!!!!!


                                                                             
    Kind Regards  Dan Gardner  1986 560SEC Euro (220kw)