84 Seville 4.1L with "Random Toyota Acceleration" issue
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HT4100 4.1, 4.5, 4.9 Discussion, 84 Seville 4.1L with "Random Toyota Acceleration" issue in Cadillac Engine Technical Discussion; Just joined up and love all the info in the forum. Hoping someone could help me out on this one- ...
  1. #1
    ryans1966 is offline Cadillac Owners Member
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    84 Seville 4.1L with "Random Toyota Acceleration" issue

    Just joined up and love all the info in the forum. Hoping someone could help me out on this one- have an 84 Seville (the one with "no trunk" as my friends call it). This started a couple of months ago and has steadily gotten worse:

    1. The Check Engine light will blink randomly here and there, but doesn't stay on for more than a second at a time
    2. When coming to a stop sign, especially after having driven a long distance at highway speed right before, the car will "surge" as I slow, almost like the accelerator is pushing itself down. Once it gets to a stop, the car will idle way down then back to normal
    3. Likes to die when idling, especially when the engine is still cold
    4. Mileage has gone down considerably as the problem has worsened

    I was told to replace the fuel filter first. This didn't make sense to me, as it doesn't starve for gas at highway speeds. TPS? Throttle Body? HELP!

    Thanks!

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  3. #2
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Is there an idle speed control motor on that car?

    Does it have cruise control?

    Those are the only 2 things that can move the throttle lever besides your foot.

  4. #3
    ryans1966 is offline Cadillac Owners Member
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Idle Speed Control Motor- No idea. Where would one look for it?

    As for cruise- it does have it, but it doesn't work. The dash lights for the cruise illuminate, but it won't engage, so I just leave it turned off and can live without it.

    Thanks for the reply!

    R

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    I don't recall the 4.1 having an ISC motor, but it's been a looong time since I've had one and could be wrong.
    the car will "surge" as I slow, almost like the accelerator is pushing itself down. Once it gets to a stop, the car will idle way down then back to normal
    Check for vacuum leaks.

  6. #5
    ryans1966 is offline Cadillac Owners Member
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Not sure if this helps any or not, but Rock Auto shows it as an available part to buy for the 84 with the 4.1L. Also, I might not have been clear on the surging thing. The car will continue to push itself at a stop sign after a period of highway driving, usually.... like it has a mind of its own and just wants to keep driving through the stop sign. If I hold the brake down for a couple seconds, it will idle way down, almost die, then it's fine. It's OK when I drive it since I know it's coming, but I'd hate to have my wife shoot out into traffic. The mother-in-law..... well, we won't discuss that! : )

  7. #6
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    The ISC motor (if you have one) is right in front of the throttle body. It has a 'screw' sticking out of it that pushes on the throttle lever.

    You say pressing the brakes makes it stop trying to go? A normally operating cruise system is supposed to disengage when the brake is pressed... Disconnect the cable that runs from the cruise control unit to the throttle body to be absolutely certain that the cruise isnt giving it gas for some reason. Someone with a 4.1 can offer some insight on the component locations and there's always rockauto if you want to see what a particular part looks like.

  8. #7
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Interesting problem. The 4.1 in my '85 has the ISC.

  9. #8
    ryans1966 is offline Cadillac Owners Member
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Pretty sure the cruise wouldn't be an issue. As I said, it only lights up but doesn't engage, so I just leave it turned off all the time. Would a malfunctioning ISC motor cause it to "push" itself? It's as if, when I'm holding down the brake sometimes, another foot is pushing on the gas pedal. It only happens for a couple seconds, then the car gives up on pushing, idles down to almost dying, then is back to normal.

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    Ranger's Avatar
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Yes it's possible. The ISC motor controls the throttle at idle.

  11. #10
    MrDobin is offline Cadillac Owners Fanatic
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    disconnect the cruise control. I had my 85 almost take off and occasionally have sudden acceleration a while back. After I messed with the cruise control and road tripped using it, the issue stopped. I doubt its the idle but I don't know the 84. Update after trying

  12. #11
    MrDobin is offline Cadillac Owners Fanatic
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Though if its idling down then up it could be multiple things... Idle control shouldn't cause mass acceleration but for sure would explain near stalling deal

  13. #12
    kdcing is offline Cadillac Owners Fanatic
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    As someone already mentioned, the ISC is a small motor w/ a screw located near the throttle. The screw will actually contact the throttle.

    The best way to confirm if the problem is in the ISC is to disconnect the ISC when the engine is idling correctly....then drive the car. If the engine surge goes away, then you know the ISC is bad, or it needs to be relearned or something related to the ISC is not correct.

    If you use this method and disconnect the ISC, be careful as the engine could stall when the engine approaches idle (especially on a cold engine).

  14. #13
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Isn't the 84 rear wheel drive?

    My 85 w/ 4.1 has ISC and I imagine all of them have it given the integral nature of the thing, but then again if it's RWD all bets are off.

  15. #14
    whereto is offline Cadillac Owners Member
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    I would set the cruise on my 83 Touring Coupe,and it would take off like a scalded ass dog!Tapped the brake pedal,reset, and would run fine.I drove it 16 yrs with no problems.

  16. #15
    carnut is offline Cadillac Owners Master
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    Re: 84 Seville 4.1L with "Random Toyota Acceleration" issue

    Do a SEARCH on this forum for adjusting idle control motor and throttle position sensor. You are describing an ISC either way out of adjustment or binding. With the car running in park, look over the drivers fender to where the throttle body is. If the climate system is in AUTO you should see the ISC shaft extend then retract as the A/C compressor cyles on then off. Easier to watch if the air cleaner is lifted up and over to the right. I'll bet it over extends causing the idle to raise too high causing the hard to stop sensation, then it retracts almost too far and the engine bogs to almost stall. This car has no idle relearn per se procedure. With the car running, you can depress this ISC shaft with firm pressure till it fully retracts then quickly unplug the electrical connector and verify .060 thou gap between it at the throttle shaft. Once we know the gap is at spec then shut the engine off, reconnect the wires to the ISC and wait ten seconds and restart. Now if working as designed, it should idle at about 600 RPM and you will see this ISC shaft extend and retract every time the A/C engages. Report back once this is done.

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