93 Seville Transmission Problem
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 93 Seville Transmission Problem in Past Cadillac Vehicle Discussion; I've had this problem for years but it seems to have gradually been getting worse. I've wanted to figure out ...
  1. #1
    ZeroOctane's Avatar
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    93 Seville Transmission Problem

    I've had this problem for years but it seems to have gradually been getting worse. I've wanted to figure out the problem and see if it could be fixed but when I've posted about it here not much came of it. I am anything but well versed in transmissions but I will explain it as best I can, so please bare with me.

    Basically if I hit the gas mildly hard (used to require almost flooring it - now just even average acceleration will do it) the car will rev up and continue accelerating up to 71mph (if I do nothing obviously) with my foot off the gas pedal. Accelerating from a complete stop on an incline seems to exacerbate the issue. This problem always happens when shifting into 2nd gear around 18mph, although occasionally it will happen going into 3rd gear. Sometimes I can feel it just starting to rev up and if I brake it will return to normal operation. I used to think this is what people referred to when they said their transmission "slipped", but I am no longer sure that is the case.

    This problem only occurs less than 1% of the time I am driving the car, but it is frequent enough to happen maybe 1 out of 4 times I take the car out for a drive. It is a serious issue especially if I need to stop at a light, as the engine will be revving high and the car itching to race forward. The way I usually stop it is to come to a complete stop, shift into neutral and then back into drive. Sometimes it takes several tries but this will return the car back to normal operation. Sometimes I can perform that fix while the car is accelerating and it will return to normal.

    Any ideas or input?

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  3. #2
    MoistCabbage's Avatar
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    A "slipping" transmission is when engine speed increases, and vehicle speed does not. It sounds like you're describing I intended acceleration.

    Are you saying that the engine revs up without you pressing the pedal? Or continues to rev after you've released it?

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    ZeroOctane's Avatar
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    Re: 93 Seville Transmission Problem

    Quote Originally Posted by MoistCabbage View Post
    A "slipping" transmission is when engine speed increases, and vehicle speed does not. It sounds like you're describing I intended acceleration.

    Are you saying that the engine revs up without you pressing the pedal? Or continues to rev after you've released it?
    Thanks for the clarification. In that case, no, it is not slipping.

    Regarding your question, yes, I am stating the latter; it will continue to rev and speed with continue to increase even after I have released the pedal, usually after a moderate application of pressure, but sometimes even under average pressure (i.e. common driving habit).

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    MoistCabbage's Avatar
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    Ok, that has nothing to do with the transmission.

    Either the throttle is sticking, the cable is sticking, or the ISC motor is malfunctioning.

    Have you pulled the codes?

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    ZeroOctane's Avatar
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    Re: 93 Seville Transmission Problem

    Quote Originally Posted by MoistCabbage View Post
    Ok, that has nothing to do with the transmission.

    Either the throttle is sticking, the cable is sticking, or the ISC motor is malfunctioning.

    Have you pulled the codes?
    Interesting, because I have had several mechanics look at the car and none was ever able to find a transmission problem. Unfortunately I've never been able to duplicate the problem in-person for them to witness.

    Funny you mention the ISC motor. About 1, maybe 2 years after I got the car in 2006 I had the ISC motor replaced because the car would sometimes die when idling. I do not remember having the "transmission" problem when I first got the car, but I do remember the problem having existed for some time. Perhaps the ISC motor is the cause...

    I have pulled the codes previously and researched them but don't remember discovering anything of significance. I will pull them again and post them up here.

    One more thing, sometimes after the issue occurs the "Service Engine Soon" light will come on, but will turn off when the car returns to normal.

  7. #6
    MoistCabbage's Avatar
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    The SES light means that a Powertrain code is current.

    Pull them and post them here with definitions.

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    N*Caddy's Avatar
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    Re: 93 Seville Transmission Problem

    Definitely NOT a transmission problem, it does what it should, transfers the engine power to the wheels.
    Now why you have the unintended acceleration...either a sticky cable, or throttle boddy or some of the sensors in the throttle body area, not sure if ISC can get the RPMs in the mid 2000's but definitely the issue is in the throttle area.
    First check if the cable moves freely, test if the throttle body is not binding, clean the throttle body, then you go after sensors, leaks.

  9. #8
    ZeroOctane's Avatar
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    Re: 93 Seville Transmission Problem

    Ok, the codes:

    P026 History - Shorted Throttle Signal Switch
    P098 History - High RPM P/N to D/R Shift Under ISC
    I039 Current - Loss of Road Sensing Suspension Data

  10. #9
    N*Caddy's Avatar
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    Re: 93 Seville Transmission Problem

    P026 History - Shorted Throttle Signal Switch
    This is what causes the issue.

    P098 History - High RPM P/N to D/R Shift Under ISC
    This is the effect and I would say be careful or you break the transmission, don't shift into gear at high RPM.

    I039 Current - Loss of Road Sensing Suspension Data
    To be considered when the above are fixed.

  11. #10
    ZeroOctane's Avatar
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    Re: 93 Seville Transmission Problem

    Quote Originally Posted by N*Caddy View Post
    P026 History - Shorted Throttle Signal Switch
    This is what causes the issue.

    P098 History - High RPM P/N to D/R Shift Under ISC
    This is the effect and I would say be careful or you break the transmission, don't shift into gear at high RPM.

    I039 Current - Loss of Road Sensing Suspension Data
    To be considered when the above are fixed.
    Thanks N*.

    So how do I go about fixing the "shorted throttle signal switch"? Is it a big project?

    Regarding your comment "This is the effect and I would say be careful or you break the transmission, don't shift into gear at high RPM." can you please elaborate? Particularly about not shifting into gear at high rpm. I don't manually shift it obviously.

  12. #11
    N*Caddy's Avatar
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    Re: 93 Seville Transmission Problem

    For the TPS you need the diagram, should be a small thing for somebody who understands electrics, can read a schematic and know how to diagnose shot and continuity in a circuit. Unfortunately I know nothing about the 4.9 controls.
    The RPM thing, you start the car and it idles high (like 3000 RPM), you shift into gear with the RPMs so high...is not good for the transmission.

  13. #12
    ZeroOctane's Avatar
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    Re: 93 Seville Transmission Problem

    Quote Originally Posted by N*Caddy View Post
    For the TPS you need the diagram, should be a small thing for somebody who understands electrics, can read a schematic and know how to diagnose shot and continuity in a circuit. Unfortunately I know nothing about the 4.9 controls.
    The RPM thing, you start the car and it idles high (like 3000 RPM), you shift into gear with the RPMs so high...is not good for the transmission.
    Yeah, I've NEVER done that. Seville isn't my daily driver and I always give it a few minutes to warm up.

    Sounds like something I can't do. I'll have to ask my mechanic. Do you it would have been when my ISC motor was replaced years ago by the Cadillac dealership that would have created this probem? I need to check my records, but I think I even brought the car into them to see if they could figure out this unintended acceleration issue, and they came up empty! Pisses me off if they caused the issue because it was like a $700 repair for the ISC motor.

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