[T3] Elusive Smooth Idle

[Bobsnotch at aol.com]

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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