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Thread: 88 deville rough idle with heater or ac on

  1. #1
    normllikeme is offline Cadillac Owners Member
    Automobile(s): 1988 Sedan Deville
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    88 deville rough idle with heater or ac on

    i'm currently battling a rough idle like many other 4.5s.
    no codes. in econ mode the idle is smooth
    and only happens with the a/c or heater on (more like a surging perhaps)..
    a/c clutch engages/disengages alot

    any thoughts?

    thanks


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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 88 deville rough idle with heater or ac on

    Heater is completely unrelated.

    Surging sounds like a vacuum leak.

    A/C clutch engaging and disengaging is normal. The interval will depend on temperature and humidity. Is it providing cool air?

  4. #3
    normllikeme is offline Cadillac Owners Member
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    Re: 88 deville rough idle with heater or ac on

    ya both the heat and a/c work normally. haven't found any vacuum leaks yet but i guess i'll check again

  5. #4
    brougham is offline Cadillac Owners Master
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    Re: 88 deville rough idle with heater or ac on

    Depending on how quickly the AC is cycling it can be a sign of a low charge. With AC running there's additional load on the engine, that's probably what the difference is you're noticing. A tune up might improve it a bit if it's been a while.

  6. #5
    drewsdeville is offline Cadillac Owners Master
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    Re: 88 deville rough idle with heater or ac on

    We'd need a better description, but if the heater and AC are being used in "auto" mode, the compressor is being cycled. That's more load on the engine, which the isc should be adjusting for. It may be inop, since you mention the symptoms don't appear in "econ" mode. Do the symptoms also appear when turning the steering wheel?

  7. #6
    normllikeme is offline Cadillac Owners Member
    Automobile(s): 1988 Sedan Deville
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    Re: 88 deville rough idle with heater or ac on

    did plugs/cap/etc recently.

    and yes now that mention it i think it does act a little off when i'm turning the wheel...i have thought about snagging a new isc motor (i'm hearing a bit of a rattling type noise from the area, just wasn't sure if it was the isc or throttle body)


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