<s>
An	O
idle	B-Algorithm
air	I-Algorithm
control	I-Algorithm
actuator	I-Algorithm
or	O
idle	B-Algorithm
air	I-Algorithm
control	I-Algorithm
valve	I-Algorithm
(	O
IAC	O
actuator/valve	O
)	O
is	O
a	O
device	O
commonly	O
used	O
in	O
fuel-injected	O
vehicles	O
to	O
control	O
the	O
engine	O
's	O
idling	O
rotational	O
speed	O
(	O
RPM	B-Application
)	O
.	O
</s>
<s>
In	O
carburetted	O
vehicles	O
a	O
similar	O
device	O
known	O
as	O
an	O
idle	B-Algorithm
speed	I-Algorithm
control	I-Algorithm
actuator	B-Algorithm
is	O
used	O
.	O
</s>
<s>
The	O
IAC	O
actuator	B-Algorithm
is	O
an	O
electrically	O
controlled	O
device	O
,	O
which	O
gets	O
its	O
input	O
from	O
the	O
vehicle	O
's	O
engine	B-Device
control	I-Device
unit	I-Device
(	O
ECU	O
)	O
.	O
</s>
<s>
The	O
actuator	B-Algorithm
is	O
fitted	O
such	O
that	O
it	O
either	O
bypasses	O
the	O
throttle	O
or	O
operates	O
the	O
throttle	O
butterfly	O
valve	O
directly	O
.	O
</s>
<s>
The	O
actuator	B-Algorithm
consists	O
of	O
a	O
linear	O
servo	O
actuator	B-Algorithm
servomotor	B-Algorithm
that	O
controls	O
a	O
plunger	O
which	O
varies	O
air	O
flow	O
through	O
the	O
throttle	O
body	O
.	O
</s>
<s>
The	O
position	O
of	O
the	O
servomotor	B-Algorithm
and	O
hence	O
the	O
amount	O
of	O
air	O
bypass	O
is	O
controlled	O
digitally	O
by	O
the	O
engine	O
ECU	O
.	O
</s>
<s>
The	O
linear	O
servo	O
is	O
most	O
commonly	O
a	O
combination	O
of	O
a	O
DC	O
motor	O
,	O
lead	O
screw	O
and	O
a	O
digital	O
optical	B-Algorithm
encoder	I-Algorithm
.	O
</s>
<s>
The	O
IAC	O
allows	O
the	O
ECU	O
to	O
maintain	O
minimum	O
RPM	B-Application
irrespective	O
of	O
changes	O
in	O
engine	O
load	O
,	O
sometimes	O
referred	O
to	O
as	O
anti-stall	O
feature	O
.	O
</s>
<s>
The	O
most	O
common	O
failure	O
mode	O
is	O
partial/complete	O
jamming	O
of	O
the	O
actuator	B-Algorithm
(	O
due	O
to	O
dirt/dust	O
or	O
even	O
oil	O
)	O
where	O
it	O
cannot	O
be	O
smoothly	O
controlled	O
.	O
</s>
<s>
The	O
result	O
is	O
an	O
engine	O
that	O
fails	O
to	O
maintain	O
idle	O
RPM	B-Application
and	O
frequently	O
stalls	O
.	O
</s>
<s>
A	O
jammed	O
actuator	B-Algorithm
may	O
be	O
freed	O
simply	O
by	O
cleaning	O
it	O
.	O
</s>
<s>
However	O
an	O
actuator	B-Algorithm
that	O
has	O
stopped	O
working	O
due	O
to	O
a	O
fault	O
in	O
its	O
servomotor	B-Algorithm
will	O
need	O
replacement	O
.	O
</s>
<s>
Air	O
leaks	O
in	O
either	O
the	O
stepper	O
housing	O
or	O
pipes	O
will	O
cause	O
elevated	O
idle	O
RPM	B-Application
.	O
</s>
