[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: Decel Valve - Nope that's not it

In a message dated 97-06-17 20:38:53 EDT, you write:

<< One tiny little extra... the decel valve... 
 The 5kCSTQs at least have one.  It is computer controlled when the throttle
 closes and bypasses the air-flow sensor, allowing the sensor plate to fall
 and cut off fuel.
 Whether this happens fast enough to make a difference is a different matter.
 It'll probably keep us amused for a while discussing it though.

DECEL VALVE:  Electrically operated solenoid that bypasses Pv air from above
the Air Flap to the Po air in the Air Box (post filter), lowering the air
flap in CIS to idle rest position.  Added to 1987 CIS + E cars (late 86 incl)
for emissions purposes.  

The decel valve opens when the idle switch is activated, a FULLY closed
throttle plate, never before.  Your rich spike will happen before the
throttle is fully closed.  The Bypass valve opens as soon as you go from
boost to vacuum.  That happens at less than full close.  The decel valve is
designed for emissions purposes only, not to aleiviate the rich fuel spike
from an open Bypass valve.  By the time the decel valve opens, the "damage"
has already been done.  Think of it this way.  All MC motors since 1987 use
the Decel Valve.  All MC CIS motors since late 1987 use a "throttle delay"
shut diaphram on the t-body spring (now this is a design that addressed
specifically the spike issue).  A lot of "stage II" cars with the Decel Valve
AND the throttle delay, STILL blow IC end caps off, lots of btdt from me and

So, no, the decel valve doesn't address the spike.  Audi added the Throttle
Delay Shut and Reinforcement Clips on the IC end caps, both addressing the
"spike" AFTER the Decel Valve was introduced.