85 Eldo HT 4100 ISC/TPS
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HT4100 4.1, 4.5, 4.9 Discussion, 85 Eldo HT 4100 ISC/TPS in Cadillac Engine Technical Discussion; I have a couple questions. I have used the search function and found valuable info, but also found conflicting info. ...
  1. #1
    85moeldo is offline Cadillac Owners Member
    Automobile(s): 2002 Cadillac STS
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    85 Eldo HT 4100 ISC/TPS

    I have a couple questions. I have used the search function and found valuable info, but also found conflicting info.

    All post I have seen say to set gap for ISC to .030 inch but this link says to set at .060 inch - http://www.ht4100.com/Diags/HT4100ISC.pdf

    Is it different based on year/model?

    Also, instead of using voltmeter for TPS setting can you use the ECC diagnostic parameter .0.1 and set to 0?

    Has anyone done mods to air intake or exhaust to help it breath better?

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    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: 85 Eldo HT 4100 ISC/TPS

    It's 0.03" for 4.9 liter. I do not think you'll be way off if you set it 0.06" though.

  4. #3
    carnut is offline Cadillac Owners Master
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    Re: 85 Eldo HT 4100 ISC/TPS

    The bottom line on the ISC is there is a gap between it and the throttle lever when at minimum idle. With the ISC fully retracted the engine will idle very low approx 450 to 500. If the lever and ISC touch, the switch within the ISC, it will continue to try to control idle speed. For more performance, you can install the larger throttle body from an 81 368 engine which has larger throttle blades. You must use the thick base gasket so the blades dont hit the intake manifold. Swap over your 2 injectors to it as well as your TPS. This gives you more air at a lesser throttle opening which gives the engine more torque around town. Yes, you can set parameters thru the on board display. Set the timing at 12 instead of 10.

  5. #4
    85moeldo is offline Cadillac Owners Member
    Automobile(s): 2002 Cadillac STS
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    Re: 85 Eldo HT 4100 ISC/TPS

    HUF & carnut - thanks for the replys.

    I must still have a vacuum leak, got a surging idle, and no way to set min air idle with that. I have replaced all hoses around intake, TB, and to canister, but still a rough and surging idle. I replaced orig TB with a rebuilt and may have over torqued bolts, not to spec just cranked em down, and tweaked base gasket.

    Carnut, thanks for info on 81 TB. May do that down the road. Right now I need to replace heater core, started leaking yesterday on way to work. Never ending saga!

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