98 Seville STS running rough
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Northstar Engines and System Technical Discussion Discussion, 98 Seville STS running rough in Cadillac Engine Technical Discussion; I have a 1998 Seville STS that had a full tune-up and new plugs and wires a month ago. Recently ...
  1. #1
    secret52 is offline Cadillac Owners Member
    Automobile(s): 1998 Cadillac Seville STS
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    98 Seville STS running rough

    I have a 1998 Seville STS that had a full tune-up and new plugs and wires a month ago. Recently it's started running pretty rough. The shifting is off and it smells like it's running rich. When I sit at a stop light, it acts as if there's still pressure on the accelerator. But as soon as the brake pedal is released, it acts as if it is going to stall. Any ideas before I have the dealership tear into it further?

    Note: the shift sensor was replaced last year.

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
    Automobile(s): 2002.5 F55 STS/65500mi, 2004 Ford F150 SuperCab4x4
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    Re: 98 Seville STS running rough

    If a dealership did a "full tune up" a month ago and the car has started acting up, you should have recourse in some sort of guarantee.

    A rich mixture could be one or more plugs misfiring, stuck injector, bad fuel pressure regulator (remove the vacuum line with the engine idling - any fuel in the line or nipple ?? - if so, new FPR time. $40 from www.rockauto.com), bad ICM/coils, incorrect spark plug wiring. Have you checked out the various vacuum lines to/from the throttlebody as well as the PCV lines at the front and rear cam covers ?

  4. #3
    secret52 is offline Cadillac Owners Member
    Automobile(s): 1998 Cadillac Seville STS
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    Re: 98 Seville STS running rough

    took the car to a cadillac dealership for other repairs. they ran diagnostics and found it was a bad ignition coil. had that replaced same day. window switches for both passenger side doors replaced today. still waiting for the console for the sunroof switch seeing as it quit working so only left with the vent now.

    did find out that my mode switch isn't working to switch between defrost, vents, floor, etc. AC is fully charged and turns on and off, mode changes on the dash, but still only blows hot air through defrost. dealership said it's a 4-5 hour job to pull the dash to get to the actuator to see if it's getting power. is there a way to check without pulling the dash? really don't want to waste time and money ($65/hr) if it's not the actuator. would greatly appreciate help and advice.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 98 Seville STS running rough

    I thought the actuator was accessible from under the dash. I could be wrong on the '98 though.

  6. #5
    secret52 is offline Cadillac Owners Member
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    Re: 98 Seville STS running rough

    The cabin filters are accessed from under the dash. From what a cadillac dealership told me, the whole dash and console has to be pulled to access the actuator. Hoping there's a way to do it without wasting time and money if that's not the problem.

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 98 Seville STS running rough

    I'm not sure, but does pre-2000 use vacuum for some of the air door/actuators ?? Start at the parking brake mechanism (crawl in with a flashlight) and see if the trip mechanism for the brake is vacuum or electrical solenoid operated...........if it's vacuum, you may have a leak somewhere......

  8. #7
    secret52 is offline Cadillac Owners Member
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    Re: 98 Seville STS running rough

    I've already checked. They are electric. I pulled the glovebox and checked the air mix door actuator on the passenger side. That one works fine. I pulled the hush panel on the drivers side and couldn't see that one, but I could hear it attempting to move. I went into the DTC and pulled the error codes. They are as follows:

    Error Codes


    IPM B1341 CURRENT (Air Mix Door Two Movement Fault)
    IPM B1344 CURRENT (HTR/DEF/AC Door Movement Fault)

    SDM B1171 CURRENT (Internal SDM Failure)

    RSS C1738 CURRENT (Exhaust Solenoid Valve Short to GND)
    RSS C1761 CURRENT (RF Position Sensor Input Fault)

    I know the SDM B1171 is for the air bag sensor. I know the passenger side has been tripped but no signal sent to deploy. Not a major concearn right now. Need to get the other 4 fixed first. If I can't find a way to fix the first 2 without pulling the dash, I'll have a huge repair bill.

  9. #8
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 98 Seville STS running rough

    I pulled the glovebox and checked the air mix door actuator on the passenger side. That one works fine. I pulled the hush panel on the drivers side and couldn't see that one, but I could hear it attempting to move.
    Try the hush panel (insulator panel) on the passengers side. If I remember correctly, the two actuators are there and only one is accessible through the glove box. The other from beneath.

  10. #9
    secret52 is offline Cadillac Owners Member
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    Re: 98 Seville STS running rough

    pulled the hush panel on the passenger side too. only able to see one mix door opening and closing as i turned the temp up and down. i'll pull it again and see if i can find the other one. part looks new tho so thinking it might've been replaced fairly recently. still trying to figure out how both the dealership and repair shop missed the last 2 codes. kinda a pain to maneuver a 5'8" 200lb body around in a small area. still need to find the htr/def/ac door so i can check that. tried cycling the defrost cycle and vents for 30 minutes and nothing. anyone know where the htr/def/ac door is located?

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