Engine rough around 1200rpm
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Cadillac STS Forum - 2005 through 2012 Discussion, Engine rough around 1200rpm in Past Cadillac Vehicle Discussion; Hey guys, So I noticed on my car, an 05 w/ Northstar, that the engine seems a little rough when ...
  1. #1
    orange57's Avatar
    orange57 is offline Cadillac Owners Fanatic
    Automobile(s): 2005 STS Northstar RWD
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    Engine rough around 1200rpm

    Hey guys,

    So I noticed on my car, an 05 w/ Northstar, that the engine seems a little rough when reved while in park from around 1000-1400rpm. I also noticed that while the RPM's are falling, it will hover at 1000-1100 for a bit before falling back down to the normal idle. Car has around 74k on it. Otherwise runs good. I'm going to try cleaning the MAF, and my replace the sparkplugs as well. Thoughts?

    thanks,
    matt

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    1crock is offline Cadillac Owners Member
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    Re: Engine rough around 1200rpm

    Check your intake manifold bolts. Loose ones are common leading to vacuum leaks, rough idle, stalling, etc.

  4. #3
    orange57's Avatar
    orange57 is offline Cadillac Owners Fanatic
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    Re: Engine rough around 1200rpm

    That was thing I checked. They are tight. What I did find, is a hose on the back of the manifold, which goes to the brake booster does not seem to be very snug on the fitting, and there is no clamp there. I believe the fitting in the intake manifold is a check valve. I will have to investigate some more.

    Thanks for the input.

    matt

  5. #4
    B1n2fra's Avatar
    B1n2fra is offline Cadillac Owners Fanatic
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    Re: Engine rough around 1200rpm

    Yes be sure to check for vacuum leaks. My hose behind the engine that looks like it connects behind the upper intake, had mysteriously fallen off after I had some work done on the car and the car idled like crap. It drove fine but I also noticed a lack of power if reved very high like a WOT and my brakes were as if the car was off. I had to codes pop up p0131 and p0151. I heard the hissing of air in the back of the motor and found my problem. Hose was in a very tight spot but with determination I reconnected it and all is well. I will try to get a clamp or something on there so I doesn't happen in the future. Its very dangerous to be on the freeway and this comes off and your brakes are damn near gone....

  6. #5
    MacMuse's Avatar
    MacMuse is offline Moderator
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    My roughness around that RPM, especially under very light acceleration, was cleared up by a flurry of dealer work (under warranty - yeah!) last year.

    Thermostat & housing seal - this was the original issue but they found more.

    Leaks in the intake manifold area - 8 runner seals replaced. Brake booster vacuum hose.


    So yeah, vacuum issues are your likely candidate. Best handled by someone experienced with a Tech2 computer, like a dealer perhaps.

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