4.9 Idling fast and intermittent service light
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Idling fast and intermittent service light in Cadillac Engine Technical Discussion; I have a 1992 Eldorado Touring Coupe. It has 139,000 miles. For a few months now it sometimes idles very ...
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    aguthmiller's Avatar
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    Exclamation 4.9 Idling fast and intermittent service light

    I have a 1992 Eldorado Touring Coupe. It has 139,000 miles. For a few months now it sometimes idles very fast after starting. Initially after statup it idles at about 1200RPMs and then quickly increases to somewhere around 1600-2100RPMs (it varies). Sometimes it will stay there and sometimes it will slow (over 1-3 minutes) slow back down to normal idle around 600-700 rpms. Also it will occassionally thow a service engine soon light. It does this more often at stop lights and usually goes back out when I take the car back off idle for more than a minute. However sometimes once it comes on (usually if it comes on during initial idle after starting) it does not go back out. Any thoughts????

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    Question Re: 4.9 Idling fast and intermittent service light

    Also, the error code that seems to connected to the problem is E041. I've found two similar definitions: 1) No Cam reference signal from ignition control module 2) Cam Sensor Signal Problem.
    Is this more likely a problem with the ICM or Cam Sensor? Is the Cam Sensor easily (and cheaply) replaced?
    Any help is very appreciated

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    Re: 4.9 Idling fast and intermittent service light

    disconnect the battery for about 10 minutes then start your car, the car might have to relearn the idle values and it also might clear out the code, my car raced too really high when i start it and now after doing this it now idles at 1500 for about 30 seconds and warms up the rest of the period at 1200 rpms.

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    Re: 4.9 Idling fast and intermittent service light

    Quote Originally Posted by 90devilleguy
    disconnect the battery for about 10 minutes then start your car, the car might have to relearn the idle values and it also might clear out the code, my car raced too really high when i start it and now after doing this it now idles at 1500 for about 30 seconds and warms up the rest of the period at 1200 rpms.
    I'll try that, but something tells me it won't help. I've already manually cleared the code (I know that doesn't cause it to relearn), and I've also replaced the battery since I've been having this problem I think (unrealated, just old battery). The code is also intermittant. The light will come on sometimes for 10-45 seconds then go out, and sometimes just at stop lights, or sometimes a whole trip.

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    Re: 4.9 Idling fast and intermittent service light

    I have had this happen several times over the years. The important thing to getthese thingss to idle is to keep the throttle body clean. The round gasket between the T.B. air horn is probably missing, replace it. a quadrjet carb air filter to carb gasket works fine and will be easire to source. To clean the T.B. , arm yourself with a can of carb cleaner, long Q-tips and clean rags. the key is to block the throttle plates open and completly clean the black deposits from the backside of the blades and the bore that they seat on. At this time you need to clean the black carbon deposits from the EGR tubes below the blades. this stuff is harded. be carefull not to break the tubes off. I have used a small drill bit to excavate the stff combined with liberal doses of carb cleaner. When I am done I wick the excess carb cleaner fron the floor of the T.B. for easier starting. After the cleaning exersize, go through a idle learn proceedure. I also apply drylube to the plunger of the idle control motor. Also having the proper fuel pressure and good injectors is important. The 4.9 injectors have a reputation for weekness. Mine have 175K on them and are fine.

    Blue_eldo

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    Re: 4.9 Idling fast and intermittent service light

    Quote Originally Posted by blue_eldo
    The round gasket between the T.B. air horn is probably missing, replace it.
    You are correct about this. I'll replace this immediately.

    Quote Originally Posted by blue_eldo
    The key is to block the throttle plates open and completly clean the black deposits from the backside of the blades and the bore that they seat on. At this time you need to clean the black carbon deposits from the EGR tubes below the blades.
    Quote Originally Posted by blue_eldo
    Also having the proper fuel pressure and good injectors is important. The 4.9 injectors have a reputation for weekness. Mine have 175K on them and are fine.
    This all sounds like a good idea (especially from what I've been reading in the forum), and I've never done this in the 85k I've owned it, except for cleaning the TB with carb cleaner once (didn't scrub it, just sprayed and let it sit). Thanks for the help.
    But still one questions remains.... What about the code 41 about the cam speed? Why would a dirty intake cause this code? Or do you all think there may be something more to this?

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    Re: 4.9 Idling fast and intermittent service light

    A couple of things.... BTW, the advice so far is not bad but doesn't address your problem I suspect. The idle learn will have no effect on this problem.

    The code 41 indicates a problem with the cam position sensor or the cam position sensor circuit. That sensor allows the PCM to synchronize it's operation of the fuel injection so that the fuel injectors inject sequentially with the intake events...i.e...the same as the engines firing order.

    Look at the distributor and look at the distributor shaft below the cap. You will see a square looking bulge in the distributor shaft housing just below the cap. It will have a cap on it with wires coming out. That is the cam position sensor. Likely it needs to be replaced as it is probably suffering from old age. Simple to replace. 4 screws I think if my memory is correct. Just unplug the wire connector on the pigtail attached to the cam position sensor, unscrew, R&R the sensor and hook the wires up. Nothing to adjust or set. You might check the connector on the wiring pigtail ahead of time to make sure that there is no corrosion or anything in there causing a circuit continuity problem.

    The cam position sensor circuit problem could possibly cause your idle speed problem. I would fix it first and see.

    If not, then the idle speed control motor may be getting lazy from old age and/or the closed throttle switch in the plunger of the ISC motor may be getting intermittantly sticky. Usually the cure is to replace the ISC motor at this point in that package's life.

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    Re: 4.9 Idling fast and intermittent service light

    BTW...you do want to clean the throttle body out as recommended regardless of the other problems. Hold the throttle blades wide open and spray and scrub the bore BELOW the blades and the back side of the blades. An old toothbrush and some carb cleaner and 5 minutes is all it takes. While you are in there, rod out the two tubes that are sticking up at you below the throttle blades. Those are the EGR delivery tubes and should not be full of carbon. Rod them out thoroughly with a piece of stiff wire. Not looking for squeaky clean here, just get the carbon out so the EGR can flow. It is normal for the tubes to sometimes be a little loose or wiggle slightly in the manifold.

    After cleaning the throttle body bores and the blades, disconnect the negative battery terminal for 30 seconds to reset the idle learn offsets so the idle speed control can start over again from the clean throttle body baseline. Just disconnect/reconnect and drive the car. Any idle "learning" at this point is greatly overrated and will happen quickly in normal driving...and has absolutely no effect on idle quality...just idle speed.

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    Re: 4.9 Idling fast and intermittent service light

    Quote Originally Posted by bbob
    Look at the distributor and look at the distributor shaft below the cap. You will see a square looking bulge in the distributor shaft housing just below the cap. It will have a cap on it with wires coming out. That is the cam position sensor.
    Having trouble locating the sensor. Which side of the distributor? Is it easily seen? And more to the point easily accessed for replacement?

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    Exclamation Re: 4.9 Idling fast and intermittent service light

    Quote Originally Posted by bbob
    The code 41 indicates a problem with the cam position sensor or the cam position sensor circuit. That sensor allows the PCM to synchronize it's operation of the fuel injection so that the fuel injectors inject sequentially with the intake events...i.e...the same as the engines firing order.
    Napa & Autozone are telling me that this car does not have a cam sensor. They say only the Northstars do (passanger side of right head). What the heck? Somehow though, on Autozone's website, the Pick-up coil comes up as a related part... (related to a part the car supposidly doesn't have?? huh?) Does the pick-up coil on a 4.9 somehow serve partially the same function as a true cam sensor on a 4.6? Also found a part called a "Hall effect switch". Did some research on this part... (http://www.actron.com/cp9087.pdf see page 2-48). Seems a hall effect switch could be used instead of a typical Magnetic Reluctance cam sensor. So am I looking for a part that Checker & Autozone refer to as a "Hall effect switch" (picture at http://www.partsamerica.com/PartDeta...pe=200&PTSet=A )? This sensor/switch looks like it would be inside the distributor, is this correct? Any help is appreciated.

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    Talking Re: 4.9 Idling fast and intermittent service light

    OK, did some more research. Got an alldatadiy.com subscription. Took like 2 minutes to find what I was looking for. Well worth the $24.95/year!!!! So the "Hall Effect Switch" IS what is used as the "cam position sensor" in a GM HEI distributor. This sensor is located directly accross from the Ignition module INSIDE the distributor just under the rotor and plate covering the inside of the distributor. It is held in by two screws and has a 3 wire connector. $76.99 for Delco version from Checker. Looks like it will take 30 minutes tops to replace (including time to get out the tools). Thanks for all your help guys (especially Bob, I thought you meant on the outside of the distrubutor though, oops). I'll replace and hope the code goes away.

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    Re: 4.9 Idling fast and intermittent service light

    Quote Originally Posted by bbob
    BTW...you do want to clean the throttle body out as recommended regardless of the other problems.
    Cleaned out the throttle body. Found one of the EGR tubes COMPLETELY clogged (the right one). The other was about 25% restricted.

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    Re: 4.9 Idling fast and intermittent service light

    Quote Originally Posted by aguthmiller
    So the "Hall Effect Switch" IS what is used as the "cam position sensor" in a GM HEI distributor. This sensor is located directly accross from the Ignition module INSIDE the distributor just under the rotor and plate covering the inside of the distributor. It is held in by two screws and has a 3 wire connector. $76.99 for Delco version from Checker. Looks like it will take 30 minutes tops to replace (including time to get out the tools).
    Replaced the "Hall-effect" type cam sensor. Code is gone. Idles MUCH better. Nice steady 750 RPMs after a 1200 RPM warm up, just like it should.

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    Re: 4.9 Idling fast and intermittent service light

    Resting the system may do the trick. Disconnect the battery and let it sit for like 10-15 mins. It may "reset the vehicle to keep it from idleing fast.

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