high idle and unstable problem

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As I now have trouble with the idle control system of
my car, an Audi 80(not quattro), 1988, with CIS-E M
fuel system, I have to fix it by myself due to the
high cost of repair by mechanics. But I don’t know too
much my car as a new driver, it is highly appreciated
if you could give me some instructions.

Thank you so much, I really need help from experts on
this fuel system.
____________________________
Problem:
 High idle speed and not stable
Once I start the car, tach needle will gradually
climbs to 1200rm or a little big more than that within
a few seconds, and then runs steadily at that speed,
instead of 1000rm(normal idle speed). Then, after one
or two minutes, the idle problem comes. The touch
needle (of engine speed) begins to fluctuate
delicately but frequently around 1200rm, and the
engine shakes accordingly.

History:
It appeared about two moth ago, but as I drive the
car, it seems that the problem gets worse day by day.
One week ago, I drove for 500miles in two days (have a
rest in the night). After this long journey, the
problem gets much worse than before: the problem
happens every time when the engine is at idle, and the
touch speed just fluctuates more frequently then
before.

Discoveries and tests by myself:
1.Code dumped
(1) 2231
-Location of problem: Idle stabilization control
limits exceeded
-Possible reasons: Adjustment of throttle, or, intake
system leaks, or ignition timing improperly adjusted
-Solution: Perform throttle adjustment, or, check
intake system, or, adjust timing
(2) 2343: Mixture control lean limit /idle NOT
OK/check idle
(3) 4431: idle stabilizer valve/ disconnected wire or
short, or, defective idle stabilizer valve/ check
wiring, or replace idle stabilizer valve.


2.Idle screw on throttle body.
When I turn the idle screw (on the throttle body )
anti-clockwise, the engine shakes, more turns, harder
the shake will be. When I turn it clockwise, the idle
problem will get less worse, but it is a pity that it
cannot be turned too much, because the screw has been
already very tight.


3.Possible problem with wiring routed to ISV.
When I unplug the harness connector routed to Idle
stabilizer valve (ISV), it is strange that the engine
can still be started without any problem, and once I
plug it in, the engine is not affected neither. Again,
when I unplug it during the time the engine is at
idle, the engine is still running.  In a word, nothing
changes. So, it seems that now the ISV cannot adjust
the air by itself and works as just like the role of a
hose.

4.Only after I have started the car for a few minutes,
the idle problem comes. In another word, during the
first one or two minutes after I start the car, the
engine speed is less than 1200rm, but then climbs to
around 1200rm and begin to fluctuate.


5.When the idle problem happens, if I switch on the
A/C, the speed of engine will fall to a lower speed
(somewhere between 1000rm to 1100rm) and can maintain
it, no idle trouble then.

6.Engine shake
Whatever when I start the engine and switch off it,
the engine will shake very shortly but obviously. This
problem has continued for more than one month. I ever
changed a motor mount but it doesn’t work at all.

7. The hose routed to intake manifold from ISV.
Both the hose and the elbow between the hose and
intake manifold are loose, not so tight. In other
words, the air can leak from them. I changed the
elbow, but it doesn’t work.

8. Hard cold start
 When the car is cold, I need to depress the
accelerator to give gas to the car; otherwise, the
engine speed will often fall and sometimes stop.


My questions:
1. What lead to the idle problem of my car?
2. What should I do if I fix it by myself?

3. Can the problem of the hose lead to the idle
problem?
4. Why can the engine be kept in good idle status once
the A/C is turned on?

5. I ever dismantled the throttle body, but I noticed
that the idle screw near the idle switch doesn’t
connect to any other part of the car; it is just a
screw only. How can the adjustment on it affect the
idle speed and stability?


Looking forward to your help!

Sincerely yours
Anthony
tomyeyu at yahoo.com


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