Actually, if the idle RPM is ~ 1500 RPM immediately after cold start,
and the idle speed does NOT decrease or change as the engine warms and
reaches normal operating temperature, then it would appear that your
AAV piston is stuck in the cold or open position. That is confirmed by
the fact that when you block the AAV intake at the left air cleaner,
the RPM drops and the engine dies.
In summary, high idle speed means too much air is getting into the
intake. Blocking the AAV intake and having the engine die indicates
that ALL of that excess air is getting in via the AAV intake (through
the AAV) and NOT from some other “vacuum leak” or opening into the
What I was trying to emphasize in my earlier post is that even though
the AAV is stuck open, that condition is NOT the cause of the engine
dying upon application of throttle once the engine warms (5 minutes or
more after cold start). If it runs fine, except for fast idle RPM for
nearly 5 minutes after cold start, and is then rough and dies on
acceleration once warm, you have a problem OTHER than the stuck AAV, as
the AAV being open JUST gives fast idle and NOT rough running or dying.
Is the TPS that is installed in your vehicle the original Black (round)
TPS, or is it the replacement Red (oblong) TPS?
I have seen a case where a similar “dying when warm” problem was
associated with a bad TPS or bad TPS wiring. A test to see if this is
your problem is to check the TPS output voltage at the Red TPS wire
with the key in position 2/run and engine off, and throttle in idle
position (don’t press throttle or turn capstan). Measure the idle Red
TPS wire voltage before starting when the engine is cold, and
immediately after turning the engine off.
If you find that the voltage was in the .30V to .40V range before cold
start, and has fallen very low (say .02 to .05V) after running and
warming, that would explain your problem. Also, after the engine
warms, and starts to die or run rough, try disconnecting the TPS
connector (3-pins) and see if the condition remains or changes.
If your Red wire TPS voltage is currently set to .39V, that is close
enough for now.
When testing the Red TPS wire voltage, pull the TPS connector apart
JUST enough so that you can get the red meter probe into the rubber
sleeve of the female socket for the Red wire pin. The male pins MUST
remain in contact with the female sockets. Place the Black meter probe
in contact with a good ground, such as the clean aluminum of the intake
manifold. Make sure the engine is OFF, but the key is in Position 2,
or Run position.
Please let us know what you find in those tests, and perhaps we can
solve your problem.
BTW, in testing the CTS, you measure RESISTANCE (Ohms) across the two
male spades of the CTS after removing the connector. As stated before,
the resistance should be in the range of 2500 Ohms at 20C coolant temp,
and 250 Ohms at 90C coolant temp.
It sounds like you measured voltage at the connector female sockets.
One of those should be 5V supply, and the other should be ground (you
found .03V which is essentially ground).
I wouldn’t worry about the O2 sensors (won’t cause the problems you
describe even if they don’t work at all) or fuel pump just yet. I
would concentrate on the CTS and TPS for now.
Your V12 is different enough that is hard to find people who know it
and can diagnose a problem. Fortunately there are enough people on
this forum who are familiar with the unusual sytems of this engine that
you are likely to find a solution here if you just have patience and
check things out. It may take some time, but the solution should NOT
George Balthrop, Clifton, VA USA
89 and 85 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: dr pike firstname.lastname@example.org
It sounds like my AAV is working correctly then. However, I forgot
to mention that the car idles around 1500 rpm (with a slight
fluctuation up and down when warm) and adjusting the screw on the
AAV inward only makes the engine rpm increase very little if at
all. Adjusting it out doesn’t seem to do much either.
I have replaced the CTS with a new one. I tested the voltage from the
connector terminals and am getting 5 volts on one spade and 0.03 on
the other spade.
Also, I tested and reset the throttle pot (it was
around .49) to .39 at idle and it increases nicely up to 5 volts.
About the only thing I haven’t checked is the oxygen sensors or the
fuel pump pressure (it is a brand new pump) at the regulator. It is
now getting to the point that I would take the car to a real
mechanic if I could find one around here (Michigan) that knows how
to work on these exotic, irritating cats.
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