ISC Motor &TPS/E30 code
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HT4100 4.1, 4.5, 4.9 Discussion, ISC Motor &TPS/E30 code in Cadillac Engine Technical Discussion; Little background, My 87 Deville(48,500 mi. was running fine,my 18 yr.old has been driving it around lately. Now I only ...
  1. #1
    dan708 is offline Cadillac Owners Member
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    ISC Motor &TPS/E30 code Help!!!

    Little background,
    My 87 Deville(48,500 mi. was running fine,my 18 yr.old has been driving it around lately.
    Now I only put mid-grade or Premium in the vehicle,I found out for the past month or two she has been putting the cheap shi t in it.
    The other night I had to pick her up because the car had stalled on her about a mile away from home.
    When i started it back up the check engine light came on and it sounded like she threw a rod,(damn) I thought.
    Checked the oil and it was only a 1/4 qt.down and clean.started it back up and the knocking/pounding sound was gone?????
    Go it home driving very slowly,and the check engine light went off but,the stop engine/ check oil level light was flickering off and on.
    I thought she might have gotten some bad gas,I put a can of dry gas in,and the 1/4 qt.oil that was low, and it seemed to run a little better,however upon driving it around for a couple of miles later in the day,it stalled on me in reverse, and the stop engine/check oil level light came back on(flickering).

    Upon doing a search on trouble codes I have found that i have an E30 code,
    ISC Motor&TPS issue
    Now onto my questions,

    1. Could the cheap gas cause the problem??

    I hate to admit it but I have very basic mechanical skills,

    2.On a scale of 1-10 (10 being the hardest) what is the difficuly level of replacing the Isc Motor and the TPS?

    and

    3. What are the cost's of the Isc Motor and the TPS parts?
    and what do you think the dealer, and or what would you,personally charge someone to do the fix??

    Sorry for the long post just wanted to make sure I covered all the bases.
    Thanks in advance for your reply's
    Dan

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    91TexasSeville's Avatar
    91TexasSeville is offline Cadillac Owners Connoisseur
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    Re: ISC Motor &TPS/E30 code

    I believe that you are faced with two unrelated problems.

    The E30 code is telling you that the throttle (blade) position is not where the computer expected it to be. In other words, either the ISC or TPS is out of calibration.

    The stop engine lamp is telling you that the oil pressure is abnormally low. This could be just a sensor or the oil pressure really is low.

    Both scenario require a diagnostic to determine the cause. If you do not have a FSM (Factory Service Manual) or the expertise to made the adjustments, it will be time to surrender the diagnostics to a qualified technician.

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    dan708 is offline Cadillac Owners Member
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    Re: ISC Motor &TPS/E30 code

    Quote Originally Posted by 91TexasSeville
    I believe that you are faced with two unrelated problems.

    The E30 code is telling you that the throttle (blade) position is not where the computer expected it to be. In other words, either the ISC or TPS is out of calibration.

    The stop engine lamp is telling you that the oil pressure is abnormally low. This could be just a sensor or the oil pressure really is low.

    Both scenario require a diagnostic to determine the cause. If you do not have a FSM (Factory Service Manual) or the expertise to made the adjustments, it will be time to surrender the diagnostics to a qualified technician.


    Thanks for the reply,
    Yeah,like i said Oil level was fine, only down a 1/2 a qt. with 2000 mi.on it since it was changed.
    Just wondering if anyone has an idea on what a dealer would charge for the fix on the ISC and or the TPS???
    I don't want to be blind sided !!!
    Thanks again in advance for your reply's
    Dan

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    Re: ISC Motor &TPS/E30 code

    The check engine light has nothing to do with the oil pressure light flickering. There is a diagnostic code causing the SES light to come on...the code 30 that you report.

    The low oil pressure warning light is an independent system and circuit and is not managed by the ECM so that would have nothing to do with the SES.

    If the code 30 is coming on it indicates that the ECM cannot maintain the correct/desired/commanded idle speed. Generally, this is a sign that the idle speed control motor has failed. On a scale of 1-10 in terms of difficulty I would say that replacing the idle speed control motor is maybe a 2 only because you need a tool of some sorts to do it...a 1 wouldn't require a tool...LOL

    Get the replacement ISC motor and R&R it. It mounts on the throttle body in plain view and with ready access leaning over the bumper.

    Forget the TPS for the moment. Not likely the problem if a code 30 was showing up. Replace the ISC motor first and see if that fixes the problem. If the TPS is malfunctioning there would likely be a code for the TPS. Absent one I wouldn't worry about it.

    The regular fuel wouldn't hurt anything or cause this situation. If the ISC motor has made it this far (18 years) then it doesn't owe you a dime and deserves replacement. Not her fault that you gave her a car with the idle speed control motor ready to fail....LOL

    If the ISC motor fails the ECM has no means of correcting the idle speed and maintaining the idle speed or anticipating loads on the engine at idle...so the idle speed will be off, possibly very low, causing stalling. The low oil pressure light could be coming on due to the extremely low idle speeds with the ISC disabled. I would address the idle speed control issue and then see if the TPS and oil pressure warning cure themselves.

    You can check the idle speed control motor operation and/or set up the new idle speed control motor by doing the following..... with the engine idling in park, hold the RPM to 2500 or so by manually holding the throttle lever open. Simultaneously, depress the plunger of the idle speed control motor and the plunger should retract. If it doesn't and/or makes grinding noises then it is failed. Replace and proceed.... Allow the plunger to retract fully until it stops. Disconnect the wiring harness to the ISC motor to freeze the plunger in the fully retracted position. Close the throttle lever to the closed bore position. The engine will likely stall and/or idle slowly around 450-500. At this point make positively sure that there is .030 to .060 gap between the plunger and the throttle lever. There MUST be clearance when the plunger is fully retracted. If not, turn the plunger to screw it in or out to get the correct clearance. ONce clearance at full retract is established, plug the wires in, cycle the key off and on several times and observe the ISC motor operating the plunger in and out. Start it up and you should be fine.

    RE: low oil pressure warning. When you are at the dealer getting the idle speed control motor, get the OEM low oil pressure switch also. It doesn't owe you a dime either after all those years. Replace it. It is located on the oil filter adapter, just beside the oil filter. It just unscrews.....simple.

    This should fix you up.

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    dan708 is offline Cadillac Owners Member
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    Re: ISC Motor &TPS/E30 code

    bbob,thanks for not shredding me about being a rookie and keeping the post lighthearted.
    I really appreciate you taking the time to walk me through the possible fix, step by step.!!!
    I'll update later this week or next on the results.
    Thanks again
    Dan

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    Re: ISC Motor &TPS/E30 code

    No prob. I only shred people that try to shred me first...LOL LOL LOL

    There is a lot of info in the archives also on the ISC on various posts. If you search using "ISC motor" or "idle speed control" or "closed throttle switch" there should be a lot of threads that have my posts in them.

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    dan708 is offline Cadillac Owners Member
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    Re: ISC Motor &TPS/E30 code

    Better late than never,,,
    This weekend I plan to change out my ISC motor,,
    quick question tho,should I purchase it thru the dealership and pay top dollar!!!
    or,is it ok to purchase it from,say an Auto Zone or the like???
    I purchased the Low Oil Pressure Switch from the dealer as I read somewhere on post I beleive from bbob that the OEM low oil pressure switch was calibrated differently than an aftermarket part.
    Just wondering if the same holds true for the ISC Motor.
    Thanks in advance
    Dan

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    dan708 is offline Cadillac Owners Member
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    Re: ISC Motor &TPS/E30 code

    Bump

  10. #9
    Murphyg's Avatar
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    Re: ISC Motor &TPS/E30 code

    I replaced my ISC in my 93 two weekends ago. I got it from the dealer for 177.00 Canadian. I didnt think that was overly expensive.

    Would like to make a suggestion though. When you disconect the wiring harness from the ISC, inspect it !
    I went through hell tryin to figure out why the new one wasnt working properly. I finally discovered that the pins were quite brittle from heat and age and one had broken on me.
    Other than that it was quite an easy procedure.

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