[T3] Elusive Smooth Idle
Bobsnotch at aol.com
Bobsnotch at aol.com
Fri Nov 21 06:46:01 PST 2014
In a message dated 11/21/2014 12:46:46 A.M. Eastern Standard Time,
cscsheridan at gmail.com writes:
What components are in play when an automatic d-jetronic fastback is at
idle. This is after initial starting and warm up, after a few minutes of
driving, waiting at a stop light, waiting in traffic. What specific
components work in harmony to produce a smooth idle? Aside from the
installation and proper configuration of the parts (plugs, points,
condensor, cap, rotor, wires) valves set, timing at zero, rpm's adjust as
close to 900 rpm as possible, but what causes the hunting, missing and
stumbling? What D-jetronic parts are in play during a warmed up idle
circuit?
The AAR (Aux Air Regulator) is the main item, as it should be closed, or
close to it after 5 minutes. The AT requires an idle speed of 950 rpm in
neutral for it's setting. But once in gear (warmed up), the torque converter
will drag the idle speed down to around 800-850 rpms. Keep in mind that IF
the AAR is still open, and you've got the idle screw set to hold 900 rpm,
that it's possible that once it's fully warmed up that your idle speed can be
lower than 800 rpms, and can cause it not to be smooth.
However, if the engine is cycling up and down (rpms rise, then engine acts
like it shuts off and drops in speed then comes back to the higher revs
again), you're above 1100 rpms on your idle setting. This can also be
described as " a hunting idle".
Missing and stumbling are related to a distributor that is not advancing.
When you had the cap off, did you remove the rotor, and add 3 drops of motor
oil to the felt pad under it? If not, then your mechanical advance isn't
getting lubed.
Keep in mind that all parts of the engine (mechanical, ignition, and FI)
all play a role in how well the engine functions. Keep in mind that any
vacuum leaks are not tolerated in the system, and can cause some of the
problems you've listed as well, since the ECU assumes there's no vacuum leaks
(they're seen as throttle movement, due to additional air entering the system),
and it's expecting a constant regulated fuel pressure. The FI system isn't
smart like modern vehicles, as it needs certain parameters to run, and is
looking for them. It doesn't automatically adjust the system for wear, or
bad timing, or anything like the modern systems do.
I hope this helps.
Bob 65 Notch with sunroof
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