2001 SLS Over Rev/Under Rev problem

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Cadillac Seville / Cadillac Eldorado Forum Discussion, 2001 SLS Over Rev/Under Rev problem in Past Cadillac Vehicle Discussion; Hi, as you all know i have a 2001 Cadillac Seville SLS, lately, it has been bi-polar, it either over ...
  1. #1
    RandyJr16 is offline Cadillac Owners Member
    Automobile(s): 2001 Cadillac SeVille SLS
    Join Date
    Nov 2012

    2001 SLS Over Rev/Under Rev problem

    Hi, as you all know i have a 2001 Cadillac Seville SLS, lately, it has been bi-polar, it either over revs (about 1500-2000rpms), getting up to about 30 mph with no gas pedal pressure, or it under revs, at about 500 rpms, and goes up and down between 500 and 550 pretty fast, but that is just when you start it, either when you throw it into drive or reverse, it stalls out, or after a little bit of driving. im not 100% sure what it is, or how much it will cost for the parts, but i need to know soon, if you could help, thanks.

    My friend john told me his thoughts on the possibilities;

    1)Fuel pressure regulator
    2)injection system has a glitch
    3)intake manifold gasket(which we opted out because it also over revs, but still a possibility)
    4)oxygen sensor

    i only had one thought, Idle Air Control unit. but i dont honestly think that is right.
    Any Ideas on what is wrong, and the cost for parts?

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  3. #2
    basscatt's Avatar
    basscatt is offline Cadillac Owners 10000+ Posts
    Automobile(s): 2003 DHS - two-2002 DHS's, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
    Join Date
    Feb 2004

    Re: 2001 Cadillac SeVille SLS Over Rev/Under Rev problem

    ANYTIME you have something weird going on with your SLS -
    the very first thing you should do is check for Diagnostic Trouble Codes -

    if you don't know how - go here and read the ENTIRE post -


    if you have any codes - post them here -

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
    Automobile(s): 2002.5 F55 STS - 67,500 miles, 2014 Explorer XLT FWD
    Join Date
    Feb 2006
    MD Eastern Shore, Kent Island

    Re: 2001 Cadillac SeVille SLS Over Rev/Under Rev problem

    .......... and the problem is not due to any of your friend's guesses.

    To learn how to check the fuel pressure regulator diaphragm for leaks, Google "cadillac forums northstar fuel pressure regulator"

    Your intake manifold has 8 individual "gaskets", one at each port, and one "plenum", the connector between the throttlebody and intake manifold. If any of the 3 band clamps or the resonator on the intake ducting from the cold air intake box to the throttlebody is loose, that will affect idle and performance. You may get ideas from the pictures in my albums (see below).

    You might want to go to Discussions, Cadillac Tech Tips and look through the pages of threads for advice on throttlebody, IAC, and EGR cleaning. Then, go up to the top black bar and read the entire Cadillac Technical Archive: There's a lot of info there you need to know. Then go down to Engines, Northstar Performance and read through the sticky posts at the top of the threads page - same for ALL the stickys just above this post ^^^.

    Pictures, circuits, diagrams of a LOT of your car and engine parts in my albums - click my username, open the profile - 2 albums, 6 pages of stuff in the left column. get a real Helm/GM service manual set for your car/year from eBay - You WILL need it.

    Costs for parts vary - most OEM parts can be had at decent pricing from Chris in parts at Rippy Cadillac over there >>>, from www.rockauto.com, and from www.gmpartsgiant.com. To learn what's built into YOUR car, enter the VIN into the box (case specific) in www.compnine.com .

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