Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

❍ Turn the IAC upside down to empty out the dirt and fluid.
❍ Repeat step 3 through 5 about 8 times.
❍ Test the IAC on the car without permanently installing it. You might have
to repositioned some hosing to accomplish this task.
If you still have problems, then either your IAC is dead and must be replaced or the
problem is somewhere else. [Editor's Note: See the IAC rebuilding procedure noted
below.] [Ian Giles] By the way, when installing the IAC the arrow points in the direction
of airflow through the valve, so it points towards the intake manifold.
Poor/Surging Idle: Idle Speed Control Motor. [Tip from Anonymous Source]
I have a 1987 model 780 with about 115K miles. Just wanted to share my
experiences:
About 10% of the time my Idle would start to surge between 200 and 1200 rpm while
sitting at a light with the foot on the brake. This up and down action would load up the
engine with fuel and it would start emitting black smoke. It seemed to be somewhat
related to engine temperature. Occasionally it would get bad enough to kill the
engine, but at highway speeds it seemed to run fine. I first looked at the idle speed
motor, but it appeared to be functioning properly when the voltage was applied to the
terminals per the normal checks. I then performed the disassembly and cleaning of the
idle speed motor as described in this web site. Even though the inside of the motor
was reasonable clean, I went ahead and polished the commutator. I detected that the
bearings that the rotor turns on were a bit gummy so I cleaned it well and lubricated it
with a bit of graphite. Ever since this little operation it has been idling like a champ. I
suspect that small bits of commutator crud and wear on the brushes may have been
creating dead spots and poor response to idle demands form the processor.
Intermittent Stalling: Faulty IAC or Hall Sensor. [Symptom:] Intermittent stalling/no
start condition on an 86 740 (b230F) manual trans: occasionally dying (engine
suddenly has absolutely no power, but the dash lights do not come on) while driving
on the expressway and around town. After pulling over to the side, the car invariably
will restart and seem to run fine. No rough idle or other problems were noted.
[Fixes Attempted:] Several months back (per list advice), I replaced the fuel relay,
which up until the last week seems to have cured the problem. Over the last couple of
days, the car has started acting up again in the same manner. Now, the car also,
when it does restart, sputters and runs extremely poor for awhile, then goes back to
normal. Also, in the driveway, I was able to get the car to reliably stall when he put on
the brakes. I replaced the idle speed motor, which seems to have affected the brakeinduced
stalling (plus the car idles much better), but not the intermittent stalling. He