[W126 Coupe] Re IDLE AIR VALVE PIPE WORK"IS YOURS LEAKING"?

[Chet Hwilka]

Hi Dan,

Just replace the hoses.
If the hoses are too soft (or too hard) they're not going to make a good
seal.  Rubber is going to break down in time, under the conditions close to
the engine.  An air hose subjected to engine heat left undisturbed for years
hardens and seals itself.  Once the hose is moved or disconnected, the seal
is broken and it's most likely going to leak.  If those are the original
hoses they lasted 19yrs, it's time...
That goes for the all the rubber involved in the air intake to the engine.

As you know, the engine requires an air/fuel mixture to run.  Fuel is
regulated, basically, by the pressure regulator and fuel distributor.  The
air is primarily regulated by the throttle valve (directly linked to the
accelerator pedal).  The idle is basically set by the throttle closed
position.  That closed position allows only enough air to get into the
engine to barely keep it running (500 rpm).  The Idle Valve is controlled
electronically by the Idle Control Unit which in turn receives its controls
for various sources (eng temp, speed, A/C, even the gear shifter, etc).
The way the idle speed is adjusted, is the Air Valve allows air to by-pass
the Throttle Valve and goes directly into the engine.  When the O2 Sensor
detects more O2 in the exhaust, it tells the fuel distributor (thru the EHA)
to supply more fuel.  More fuel increases engine speed.

So with the throttle closes at idle, any extra air that is sucked into the
engine that by-passes the throttle is going to increase engine speed.
That's any leaks in the any of the hoses after the Idle Valve.  Those hoses
are, the little one from the IV to the metal housing that the Cold Start
valve mounts to, from there to a "Y" hose that connects to the left air
manifold hose.  The other leg of the "Y" goes to a cross-over hose, that is
routed under the air/fuel mixture unit to the right air manifold hose.
Those air manifold hoses connect to each fuel injector holders that are
secured to the head by clamping the injectors down.  The holder has a rubber
o-ring sealing it with the head and the injector has a rubber seal, sealing
it to the holder.
Any of those connections are sources for extra air..

Also after the throttle there's a lower air plenum that's connect to the
intake manifold through 8 rubber "O"  ring seals. Again a source for extra
air that didn't find it's way to the engine through the throttle.

Long story short.. Rubber is not going to last forever and has to be
replaced in time, it's cheap.  You can't fault MB for that.  The original
unclamped design lasted this long without leaking problems. Now if you've
recently replaces the hoses and they leak, then the hoses are at fault.  If
so, were they MB or after market?

Hope this helps and sorry for the looong reply..  Must be the coffee..:)
Chet