96 Deville won't idle down, hard start and backfires when cold - Page 2
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Northstar Engines and System Technical Discussion Discussion, 96 Deville won't idle down, hard start and backfires when cold in Cadillac Engine Technical Discussion; My car is a pre-OBDII 96 model. Does that make a difference?...
  1. #16
    magistrate_apeman is offline Cadillac Owners Member
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    My car is a pre-OBDII 96 model. Does that make a difference?

  2. #17
    Ranger's Avatar
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    No. In fact, it might be the 4.9 that had that, but again, I'm not positive. I AM positive that yours does not have that feature.

  3. #18
    magistrate_apeman is offline Cadillac Owners Member
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    OK. If not a relay, and thoughts as to where I should look? Where are those relays and things, anyhow? I know where the regular fuse box is on the fender well, but I didn't see the other that's mentioned in the manual.

  4. #19
    magistrate_apeman is offline Cadillac Owners Member
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    Took the girlfriend out this afternoon in the Caddy. Ran beautifully for a while, then the buzzers began buzzing. PC0717, turbine speed sensor. Wonderful. Then it sped up on its own again, briefly, and then settled back down. Gonna try tps swap tomorrow. Then, come Monday, begin hunting for someone to fix that stupid sensor at a reasonable price. BahHumBug.

  5. #20
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    P 0717 is "Input Speed sensor circuit". You might want to open and clean the main transmission wiring harness connector first. Down low below the water pump/water pump cover area.

    FWIW, to replace the ISS requires removing the transmission from the car.

    The GM cost is a bit over $100 for the sensor and 12 hours labor.

  6. #21
    magistrate_apeman is offline Cadillac Owners Member
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    Yeah, I've been researching it since last night. Found the part for a whopping $26, but there's no easy fix. Gonna begin interviewing mechanics on Monday. There's a little transmission shop down the road from me that I've got a good relationship with. Hopefully they'll cut me a deal.

    Anyone know how to locate the wire and plug in for this sensor on the outside of the transmission? I'm fixing to crawl under the car and check out the air compressor, so maybe I can find it and clean it, just for a laugh...

  7. #22
    magistrate_apeman is offline Cadillac Owners Member
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    Somehow I missed Submariner's post earlier. I was just under the car and could have checked that harness. I was looking for it on the driver side. Damnit...

    Couple questions:

    Could the idle air control valve cause my high idle? The car was idling fine earlier. I pulled the iac off to inspect it again, and I gave it a little shot of WD-40 and let it sit. Is the rod supposed to have any travel or wiggle? Anyhow, I reinstalled it, started the car and it wouldn't idle down again. Throttle body is spit-shined, including the hole for the iac.

    Looked at the air compressor and rear shocks. They're pretty rusty looking and the passenger side has a broken airline. The compressor makes a lot of racket and looks like a pain in the rear. Question is, if I purchase and install the Monroe conversion kits 90008 and 90009, will I still constantly get the annoying "service ride control" message?

  8. #23
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    Quote Originally Posted by magistrate_apeman View Post
    Could the idle air control valve cause my high idle?
    Yes. It is an air bypass circuit. The valve controls the amount of air bypassing the closed throttle plate. Is the plunger in good condition?


    Is the rod supposed to have any travel or wiggle?
    It moves in and out to control air flow. Not sure if there is any wiggle to it or not though. Never had to pull mine.

  9. #24
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    The transmission connector IS on the rear (driver's) end of the engine. So is the water pump and the water pump drive system/thermostat.

  10. #25
    magistrate_apeman is offline Cadillac Owners Member
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    Hahaha. I thought the water pump was on the passenger side wrapped up in all that accessory drive mess.

    My iac plunger doesn't move in and out at all by hand.

    ----------

    Let me rephrase that. The iac did wiggle a little, but there was no throw. The plunger didn't slide in and out at all, it just had a slight bit of slop in it, it felt.

  11. #26
    magistrate_apeman is offline Cadillac Owners Member
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    And what if I wanted to install a new air compressor; could I install new non electric air shocks and get rid of the "service ride" message?

  12. #27
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    Either install the new compressor assembly and repair the air lines - cross your fingers for the shocks - they're expensive, OR look in the Monroe catalog for new shocks with air bladders - you can run the air lines/valves (like tire valves) into the trunk and manually control rear ride height.

    You need to do some resistor work in the shock electrical connectors to get rid of the suspension system messages.

    Down in Cadilac Tech Tips or in one of the many threads in this forum over the past year. Google "cadillac forums 1996 deville suspension height control" or similar, always using "cadillac forums .........................." in the request.

  13. #28
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    Quote Originally Posted by magistrate_apeman View Post
    My iac plunger doesn't move in and out at all by hand.

    ----------

    Let me rephrase that. The iac did wiggle a little, but there was no throw. The plunger didn't slide in and out at all, it just had a slight bit of slop in it, it felt.
    It's not supposed to move by hand. It is electronically controlled and operated.

  14. #29
    magistrate_apeman is offline Cadillac Owners Member
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    These worth a darn? They come with resistors and whatnot, and allow me to keep my leveling system. $316 for the pair with free shipping on amazon: https://www.arnottindustries.com/par...28_gid110.html

  15. #30
    magistrate_apeman is offline Cadillac Owners Member
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    Monroe's tech support emailed me and said their suspension packages include instructions for disabling the dash messages, too.

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