FAQs about Fuel Injector Idleing System.

  • My idle is intermittently between 900 and 1200 rpm, why?
  • Some notes on the Constant Idle Speed.
  • What can I do about a cold idle problem?

  • My idle is intermittently between 900 and 1200 rpm, why?

    Date: Wed, 22 Jan 92 15:13:04 EST
    From: mm@lectroid.sw.stratus.com (Michael Mahler)
    To: marty@nynexst.com
    Cc: volvo-net@me.rochester.edu
    Subject: 84 GLT Idle speed problem

    > After 190k miles of running like a clock my '84 244 GLT is beginning to show
    > its age.

    Volvos don't "age", they "break-in gracefully".

    >The idle speed has been a steady 900 rpm for years. In the last month idle rpm
    >has started to vary intermittently between 900 and 1200 rpm. No consistent
    >pattern has emerged that I can see; warm weather, cold weather, day, night,
    >rainy, etc. I have checked for a bind in the throttle linkage, and
    >disconnected the auto-speed control but that didn't help.


    Anyway, you need to check a few things:

    1) When's the last time you replaced the oxygen sensor?

    2) Check the micro-switch that activates when the throttle is closed. You set it with a feeler gauge, but for now, adjust it so it JUST clicks when you close the throttle.

    3) You'll need to be sure your Constant Idle System is working:

    a) Check the fuse.

    b) Check the wiring harnesses.

    Under plastic panel, passenger side.

    IF it's working, you'll need to check the inputs it's receiving. Let me know if you want to know what these are.


    Date: Wed, 22 Jan 92 15:49:13 EST
    From: wiegman (Herman L. N. Wiegman)
    To: marty@nynexst.com
    Subject: Re: Idle speed problem


    I would guesse that there is nothing major wrong.

    A car will idle high or low depending upon a few parameters;

    1) timing, 2) fuel mixture, 3) air flow.

    1)The timing is easily adjusted or monitored. Just take a peek at it durring the eradic behavior and see if it varies more the 8 degrees on either side of 10 DBTDC. Usually the timing will vary 4 or 5 degrees as the engine is modulated around 800 rpm. If you don't have a timing light you can forget this step.

    2)The Fuel Mixture.. .well this one is hard to monitor, but you can listen to the modulation of the fuel pump. And maybe check the screw which grounds the Fuel Injection Box in the passenger side foot well (by the door hinge).

    3)The air flow is critical, so are the leaks in all of the vacuum lines! If more air is let into the intake manifold the rpms will rise. The Const Idle Sys. is a straight forward system which automatically controls the amount of air "leaking-by" the trottle plate. There are a few wire connections to the control box (the size of 4 compact disks cases stacked on top of each other). These wires go to the Air control valve (just below the first intake runner, and the shape of a tommato paste can), the coolant temperature sensor, power leads, and ignition lead.

    I would clean the leads, check some hoses (just a random inspection of the hose terminations would be ok. I find that high milage or old cars have leaks around the ends of the hoses. A few small hose clamps may be an order.) Then I would clean the electrical contacts of the CIS box.

    best 'o luck,


    From: mvao@mvgpk.att.com
    Date: Fri, 24 Jan 92 10:07 EST
    To: att!me.rochester.edu!volvo-net
    Subject: Re: 84GLT Idle speed problem

    From: "John Abt" <johna@gold.gvg.tek.com>

    While we're on the subject, my '81 GLT does an idle thing only on cold mornings. It starts up and idles fine for about 15 or 20 seconds - then the idle drops, recovers and overshoots, and then the cycle repeats. Fortunately this little oscillation is critically damped :-) - it dies out after about 4 or 5 cycles. If it's real cold (28F here in Calif), it will die with the first idle drop. The rest of the time the idle is dead-nuts (that's a tech term) on 900.

    I haven't checked anything yet. Oxy sensor, right Michael??

    John Abt

    How 'bout a vacuum leak somewhere? If your fuel/air ratio is lean, the mixture is more difficult to fire. I suspect that I have a leak, but I can't find it (I just got some injector seals, but haven't put them in yet).

    I eliminated this same idle oscillation problem by slightly enriching the default fuel/air ratio in the fuel distributor (with a 3mm allen wrench, I think). I theorized that this makes sense, since the lambda system will compensate for a lean mixture once the engine heats up enough to recongize the O2 sensor readings.


    Date: Tue, 28 Jan 92 10:21:49 EST
    From: marty@nynexst.com (Marty Baade)
    To: volvo-net@me.rochester.edu
    Subject: '84 GLT idle speed problem (solution)

    Thanks to Tim, Herman, Eric, and Michael for the many things to look at while attempting to fix my faulty idle. A kindly friend also loaned me a manual that described some of the inner workings and test procedures. By this time the idle had worked its way up to a solid 1700 rpm and I spent the following four hours testing:

    1) throttle switch for continuity and adjustment w/light & ohmmeter.

    2) coolant sensor - mounted in the worst place! w/ohmmeter

    3) air control valve - mounted in the second worst place

    4) vacuum hoses - visually - no breaks found

    5) Gumout on the throttle plate area - some junk found there

    6) oxygen sensor - disconnected - no difference noted

    7) firewall connector - clean

    8) air filter & housing - seated correctly & closed

    9) plug connections to electronic control unit - clean

    Having exhausted my knowledge and patience and most of my body heat I decided to pack it in. The complexity of the system and the lack of documentation and knowledge/experience about how it really works were just too much. I drove over to Volvo on Monday morning and threw myself on their doorstep. They replaced theair control valve, the coolant sensor and a small relay on the left fender well near the coil (which wasn't in the manual). My son bailed it out on Monday afternoon for $265 and it appears to be running as sweet as ever.



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    Some notes on the Constant Idle Speed.

    Date: Thu, 30 Jan 92 11:12:00 EST
    From: wiegman (Herman L. N. Wiegman)
    To: bever@erim.org
    Subject: Re: Constant Idle Speed sys


    don't fret! there are always alternatives! ..i think a guy named Kirk said that...

    If the sensors check out.. then why does the car settle after the temp has warmed? could it be the sluggishness of the cold car? probably...Once warm most Volvo's settle in to a constant idle .. some vary all over the place due to vacuum leaks or faulty intake components.

    Some notes on the CIS system (const. idle speed):

    There are 4 components; 1) control box, 2) air valve, 3) trottle switch and a signal from the coolant sensor.

    Once the trottle switch is engaged (the gas pedal is released all the way) the micro switch enables the CIS control box to do its thing.

    The control box looks at the car's temperature and the signal from the coil (pin one of the ignition coil) to see if the car is running and to see what rpm it is running at.

    The control box than sends the appropriate signal to the air control valve. The air control valve simply lets more or less air by the throttle plate to adjust the idle up or down.

    It is my experience that the air control valve gets stuck or wears out. Used ones are available from the vendors in the PPL (I will list some below). the control boxes will also be available from them.... ? $30?

    On latter models there is a screw below the trottle plate which can compensate for a poor air valve. I'm not sure that your '82 has one. Other things that should be checked! are the timing and all electrical connections.

    You can easily change these components yourself with a phillips screw driver and small plyers. (do you have a manual? ..best $12 deal there is.)

    best 'o luck,


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    What can I do about a cold idle problem?

    Date: Thu, 26 Aug 1993 14:33:53 PDT
    From: damouth@wrc.xerox.com (David E. Damouth)
    To: swedishbricks@me.rochester.edu
    Subject: B230FT cold idle problem

    For several months, the 1986 745T (B230-FT engine) has been gradually acquiring a little stumble just after a cold start. It tended to stall when put in gear (automatic transmission), unless helped along a little with the accelerator. Even when warm, the idle speed controller tended to hunt a little, where it used to be rock stable.

    Two days ago, I finally noticed another symptom: the manifold pressure gauge ("turbo" gauge) was hardly responding at all. In retrospect, I think it's been sluggish for quite a while and getting worse, but I seldom look at it.

    Given this clue, I tracked the vacuum line from the gauge back to the intake manifold (a non-trivial task), and discovered a hole in the rubber hose, where it is stressed by a sharp bend right at the manifold nipple. Splicing in a new piece of hose fixed the gauge, and based on two days of observation, also seems to have cured the idle problem!

    Random notes for the archive:

    the gauge hose connects to a nipple in the inner center section of the intake manifold - towards the engine, one of a group of several hoses there.

    the manifold overpressure limit switch shares the same vacuum hose. The junction is buried high up above the steerig column and the audio power amplifier where you can't possibly reach it without removing the amp. This switch is mounted on a bracket just above the pedals. I chose to splice the hose in the engine compartment rather than struggle to replace the whole thing. The rubber seems like new except near the engine.

    the vac hose for the brake-sensing switch on the cruise control comes through the firewall at the same point.

    A large, usually well equipped, auto parts store didn't have anything with which to join two hoses together. I improvised a coupler from a short piece of brake line.


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