95 deville 4.9 rough idle after warm
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 95 deville 4.9 rough idle after warm in Past Cadillac Vehicle Discussion; Needing some help, my caddy just started acting up again, error code po48 i think. Stalled one day when my ...
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    cadillac_layne86's Avatar
    cadillac_layne86 is offline Cadillac Owners Member
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    95 deville 4.9 rough idle after warm

    Needing some help, my caddy just started acting up again, error code po48 i think. Stalled one day when my wife was driving, she said it wouldn't restart immediately. By the time i got to her it would restart. So i drove it home, after about five minutes it started to run a lil rough . Then at stop signs idle was rough. After giving it some hell (thinking maybe fuel filter was clogged) i let it sit for bout an hour, and it was fine. But as soon as it warmed up it starts to run rough again. What could this be. Daily driver.

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    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    Code definition?

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    I think its egr code not sure

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    It has 246xxx miles on org motor, when i checked under hood to look at throttle body ,i sprayed tb cleaner in the tubes, ran fine until i started to drive for a little, could it be a ground cable ?

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    Re: 95 deville 4.9 rough idle after warm

    Go up to the DTC Sticky at the top of the forum page. Use the OBDI link to get the code definition. Cut and paste it here.

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    cadillac_layne86's Avatar
    cadillac_layne86 is offline Cadillac Owners Member
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    I looked up code and it said egr malfunction?

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    How do you replace the egr on this car? Its still doing the stuttering thing i drove it today and i still have lots of power but engine runs like crap. By the way my gas mileage is normal i guess, 13.4 in city.

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    Re: 95 deville 4.9 rough idle after warm

    Replacing the EGR valve on that car is difficult without removing the TB first.

    The EGR is not a monitored device on the 4.9, but the EGR solenoid and control valve are. The EGR valve itself is generally pretty reliable.

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    brougham is offline Cadillac Owners Master
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    Re: 95 deville 4.9 rough idle after warm

    The EGR itself is vacuum and isn't monitored but a sensor could be picking up a value that is telling the computer the EGR isn't working properly. It wasn't too hard to change on my 94 with the right tools, but you need to figure out what part of the system isn't working properly before just changing random parts.

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    cadillac_layne86's Avatar
    cadillac_layne86 is offline Cadillac Owners Member
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    So would the sensor make the car run rough ? Or is it mainly the egr itself causing the problems?

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    MoistCabbage's Avatar
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    No, the sensors are doing their job. It's a faulty/dirty valve, or clogged passages.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 95 deville 4.9 rough idle after warm

    Years ago I got an EGR code when my catalytic got clogged. How is your exhaust flow? Does it sound any different? You already cleaned the EGR tubes, right? At 250k, the engine just may not be making sufficient vacuum any more. I would check the vacuum anyway.

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    Well the exaust sounds fine, but ya nevr kno til u take it to a muffler shop. This was more like an "over night " situation. Is there any way to test the EGR ?

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    Re: 95 deville 4.9 rough idle after warm

    Yes, on an OBDI system you can test it via the onboard diagnostics, but you'll need a FSM for the procedure. It will test the solenoid, not the valve itself as it is vacuum operated. If you reach under the EGR valve with your finger and press on the diaphragm while idling, it will open the EGR valve and stall the engine. If by chance that valve is carboned up and not seated real good, it may cause a rough idle.

  14. #13
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    Re: 95 deville 4.9 rough idle after warm

    The O2 sensor is the reference sensor for EGR operation. The computer does the EGR test every couple of hundred miles. The test is done by the computer at those intervals when the car is cruising. The computer commands the EGR off for a short time and looks for a change in the O2 output. If there is no change it will set the code.

    Try cleaning the passages in the throttle body, and try cleaning the EGR valve itself before you replace it. To access the valve I'd always unbolt the throttle body, remove the transmission vacuum modulator line and lift up the throttle body a little bit. While I'm holding the throttle body up with my left hand I would squeeze my right hand underneath it and loosen the EGR bolts with a 13mm wrench. Then I'd put the throttle body down on the block and will remove the EGR bolts. Once I'm done cleaning/replacing the valve I'd install everything in reverse order. Make sure you do this with the engine cold or you'll burn your hands. Also, you can try removing the throttle body completely if you want to mess with removing the rest of the vacuum lines and then putting them back on when you're done.

    It's been almost two years since I had the same code. I tried cleaning the valve a couple of times but the code kept coming back. When I got the replacement valve I compared how smoothly I could move the diaphragm by hand, and the old valve required a lot more muscle to lift up. So, my conclusion was - the old valve had gotten a stiffer diaphragm spring, which the vacuum could not operate. It's been been good ever since I put the new one on.

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