1993 Eldorado dies in traffic with foot off the gas
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1993 Eldorado dies in traffic with foot off the gas in Past Cadillac Vehicle Discussion; ...
  1. #1
    tedgley is offline Cadillac Owners Member
    Automobile(s): 1993 Eldorado
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    1993 Eldorado dies in traffic with foot off the gas

    Car is a 93 Eldorado base model with the 4.9. It runs fine most of the time. Recently, car just quit on the way to work. I had it towed in and they ended up replacing the ignition module. Car ran fine, with one exception…

    Occasionally, and usually after cruising along the street with light throttle pressure, when I would take my foot off the accelerator, the car rpm would drop down to 400-500 rpm or sometimes die altogether. Have to shift into neutral and re-fire the car. Car always restarts. I would say this happens 1 out of every 10 times you have your foot on the gas and then let off. 9 times out of ten, the car will settle back down to about 700-750 rpm. Then, that 1 out of 10, it will just die if I don’t see the rpm drop and “catch” it with the accelerator. I can rev the engine back up and sometimes, it seems to correct the problem, other times it still wants to return to about 400 rpm and eventually die.

    Now the REAL problem:

    I pulled the codes:

    I039 .......................................... Loss of Road Sensing Suspension Data
    I052 .................................................. ..... Keep Alive Memory Error
    P026 (E026) ......................................... Shorted Throttle Signal Switch
    P052 (E052) .................................................. ..... PCM Memory Reset

    So, I figure I will just replace the TPS. Ordered the part. Got the ACDELCO part from RockAuto ($40 shipped). I tried to follow the TPS installation instructions I got here:

    To install:
    4. With the throttle valve in the normal closed idle position, install the TP sensor on the throttle body assembly.
    5. Install 2 TP sensor attaching screws with retainers. Do not tighten the screw until the TP sensor is adjusted.
    6. Install the TP Sensor connector. Adjust the TP Sensor and perform the idle learn procedure.
    7. To Perform the TP sensor adjustment.
     Disable the generator by grounding the green harness connector plug adjacent to the generator.
     Start the engine, enter diagnostics, and select PCM override PS103 'ISC Actuator'
     Press the 'COOLER' button on the CCP to retract the ISC Actuator. This action will disengage the A/C compressor and command the EGR 'OFF'. The Climate control center display will change from '50 to 00'. The ISC Actuator will slowly retract (about 20 seconds) to a fully retracted position. Verify that the throttle lever is resting on the minimum idle speed screw. With the ISC Actuator plunger fully retracted, disconnect the ISC harness.
     Select the PCM data PD01, 'TP Sensor', while still in PCM override PS03. Note the throttle position (in degrees) displayed on PCM parameter PD01.
     (-0.5° TO + 0.5°)
     No TP sensor adjustment required. Reattach the ISC Actuator harness and disconnect the grounding wire at the generator.
     TP Sensor (-10.0° TO -0.6°) or TP Sensor (+ 0.6° TO + 90.0°) TP Sensor adjustment required.
    8. With the engine 'OFF' and the ignition 'ON', reenter diagnostics and select PCM override PS03 'ISC Actuator'. Press the 'COOLER' button to retract the ISC Actuator the minimum air setting.
     Loosen the TP sensor screws just enough to permit the sensor to be rotated. Open the throttle slightly and allow the throttle lever to snap shut against the minimum air screw. Adjust the TP sensor so the parameter display is 0°. Tighten the TP sensor mounting screws with the sensor in the adjusted position. Recheck the parameter to be sure the TP sensor parameter is (-0.5° to + 0.5).
    5. Install the air cleaner.


    Now, I start running into issues. First off, there isn’t a PS103 override. Finally, figured out that there was a typo in the instructions and they actually meant PS03. Everything went fine until I get the step to press “COOLER” When I did this, the idle RPM would keep dropping as the ISC plunger retracted until, at about 350-400, the car would just die. After doing this a couple of times, I just let the car die and continued with the process of waiting until the ISC plunger retracted all the way, disconnecting the ISC, and then checking the PD01 to make sure the voltage for the TPS was correct. Then I started the car.

    RPM (at “idle”) immediately jumps to about 2800. So now, I screw in the plunger screw on the ISC to get the idle down.

    I could go on-and-on, about how I tried this and that, but the bottom line is this;

    1) I could not follow the above instructions initially because the car kept dying.
    2) I have jacked with the ISC plunger screw to the point that I don’t have any idea if it’s anywhere close any more. The screw sticks out of the plunger about ¾ to 7/8 of any inch now.
    3) The ISC plunger is VERY inconsistent in how far it retracts and how long it takes each time I do the PS03 override and hit the COOLER button. Sometimes the plastic plunger goes completely down in the housing, other times, it still has ¼ inch sticking out (I’m talking about the plastic part here, not the metal screw). Sometimes is takes 20 seconds, sometimes it takes 2 minutes to retract.
    4) I have no idea if I have the TPS anywhere close to being set correctly. I did display the diagnostic code PD01 and adjusted the sensor until the reading was 0.2, but that was with the engine off and not having gone through the entire process.
    5) In step 7 above, it says “Select the PCM data PD01, 'TP Sensor', while still in PCM override PS03”. How in the world do you do this?
    6) I finally decided that, to be able to drive my car from the shop to my house (about 4 miles), the best this I could do was unplug the ISC and drive it. I unplugged the ISC and hit the starter. Now the car will not even turn over. I don’t know if it has some safety catch built into the computer to prevent starting or the battery finally got too low. The only other thing to note is that the ISC plunger is sticking WAY out. Maybe the car won’t start with the throttle open that much. Anyway, I ended up putting the charger on the battery and walking home at midnight (took me a hour and 20 minutes).

    I know I’m just rambling now. Sorry for the long post. I would appreciate ANY help with getting my Caddy back on the road. I inherited it from my aunt who passed away a year ago. It has 50K miles on it and clean as a pin. Literally, was owned by “a little old lady who bought it new and only drove it on Sundays”.

    PS. With the erratic behavior of the ISC, I’m starting the think it may be bad, even though there was no code thrown for that.

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
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    Re: 1993 Eldorado dies in traffic with foot off the gas

    P026 is your problem. The PCM is not being told that the throttle is closed so it is not advising the ISC motor to control the idle.

  4. #3
    tedgley is offline Cadillac Owners Member
    Automobile(s): 1993 Eldorado
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    Re: 1993 Eldorado dies in traffic with foot off the gas

    I have spent hours today looking for an answer to this problem. I think I initially have misunderstood that the P026 means the Throttle Switch in the Idle Speed Controller, not in the Throttle Position Sensor. May have replaced the TPS for nothing...

    I am going to take the ISC off tomorrow and clean it real good and see if that helps. If not, I guess a new ISC will be next.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1993 Eldorado dies in traffic with foot off the gas

    Open and clean the contacts in the ISC motor closed throttle switch. It may be a different name for the same switch.

  6. #5
    STS_Seville_Hunter is offline Cadillac Owners Enthusiast
    Automobile(s): 91 ETC, 91 STS, 98 Eldo Convertable, '93 Seville
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    Re: 1993 Eldorado dies in traffic with foot off the gas

    However my Eldo has the same code and it always appears at the same rpm even with the isc disconnected, has me at quite a loss.

  7. #6
    tedgley is offline Cadillac Owners Member
    Automobile(s): 1993 Eldorado
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    Re: 1993 Eldorado dies in traffic with foot off the gas

    Quote Originally Posted by STS_Seville_Hunter View Post
    However my Eldo has the same code and it always appears at the same rpm even with the isc disconnected, has me at quite a loss.
    Obviously, I am not an authority on this, but your issue sounds like it may be a problem/short in the actual wiring...although that probably wouldn't account for it always happening at the same RPM.

    Actually, at this point, as far as my car is concerned, I'm more worried that the starter wouldn't even turn over last night. Hope I didn't fry something else in the wiring.

  8. #7
    tedgley is offline Cadillac Owners Member
    Automobile(s): 1993 Eldorado
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    Re: 1993 Eldorado dies in traffic with foot off the gas

    I got the ISC off today and took it apart. The throttle switch contact arm was loose and flopping around. I just went to O'Reilly's and got a new ISC for $67. Installed and car runs fine now. No codes so far, but will keep a close eye on this week. Thanks for the replies.

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