96 Deville won't idle down, hard start and backfires when cold - Page 4
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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; Spray some Brakleen around every possible vacuum leak point (incl manifold mounting and the over pressure relief valve). Listen for ...
  1. #46
    Ranger's Avatar
    Ranger is online now Cadillac Owners Member
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    Spray some Brakleen around every possible vacuum leak point (incl manifold mounting and the over pressure relief valve). Listen for an RPM increase.

  2. #47
    magistrate_apeman is offline Cadillac Owners Member
    Automobile(s): 1996 Deville Base
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    Received new iac valve. It came in the wide open position. Installed, now car revs immediately to 3000 rpms.

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    Pulled irc plunger out by hand. Plugged it in while in hand with key on, and the unit pulses and vibrates against pressure applied to the plunger, but doesn't noticeably draw in and out. Checked two old iac valves the same way, and they reacted similarly. Reinstalled new iac with plunger pulled out. Idle back to 1500. $60 wasted. Lost.

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    Also sprayed carb cleaner around intake and any vacuum lines I could find... Nothing. Disconnected some vacuum lines while car was running, no drastic changes.

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    Disconnecting the tps gets the idle down to 1175

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    Pulled the air intake line off the mafs housing, then gradually choked off the engine's air, and now it's idling smoothly at 750.

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    Plug the tps back in, and it goes wild again.

  3. #48
    magistrate_apeman is offline Cadillac Owners Member
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    Installed another new tps, and now the car seems back to normal. Grrrrrrrrrrr

  4. #49
    magistrate_apeman is offline Cadillac Owners Member
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    No more unbranded Autozone junk for me. Car is running fine again.

  5. #50
    magistrate_apeman is offline Cadillac Owners Member
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    Anyone know what would cause me Deville to start shifting into overdrive too early, and shifting frequently between drive and overdrive while trying to maintain a steady speed between 50 and 60? Please tell me it's something simple like a shift solenoid accessible thru the pan. Please please please. No codes and the car has been running great.

  6. #51
    stoveguyy is offline Cadillac Owners Connoisseur
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    Hmm, my car goes into OD at 45mph and never drops down to 3rd. I have 3.7 final drive though. I assume urs is 3.1 or so?

  7. #52
    magistrate_apeman is offline Cadillac Owners Member
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    I don't know, stoveguy. Where would I look for that particular info?

  8. #53
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    The '96 Deville has an LD8 motor so it is teamed with the 3.11 final drive. When it shifts into OD (4th gear) will vary depending on load. TCC lock up is at 41 MPH, but it will also vary with load. Neither should toggle back and forth while at a steady cruise speed. Not sure what would cause that though.

    First thing you need to clarify is are you talking about OD or the TCC?

  9. #54
    stoveguyy is offline Cadillac Owners Connoisseur
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    Yes, most folks cannot tell when tcc drops off since its only 2-300 rpm. BUT u will notice OD dropping off. Hwy cruise is 2k? Jumping up to 2800rpm WILL get ur attention.

  10. #55
    magistrate_apeman is offline Cadillac Owners Member
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    Stopped and talked to a transmission guy I know (who unfortunately refuses to touch a Northstar equipped machine) and he says the torque converter is dropping in and out of lockup for some reason, not shifting from drive to od as I originally claimed. As ranger says, the issue begins at 41mph. Doesn't seem to do it much if at all with cruise control engaged, but is very noticeable when trying to maintain speed between 41 and 60 via foot. Further thoughts? Simple solution, perchance?

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    Could a faulty brake light switch cause this issue? I noticed a few days ago that all my lights had started dimming when I apply the brake pedal, and just now I've begun getting a funky clicking noise from the brake pedal. Also, I can hear an obvious load being put on the engine when I depress the pedal.

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    AND, the switch only clicks funky when in park with the engine idling. AND, my trip odometer and fuel mileage gauge reset on their own after reaching around 300 miles, if that means anything.

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    AHA! http://www.amazon.com/gp/product/B00...w_bottom_links

  11. #56
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    Re: 96 Deville won't idle down, hard start and backfires when cold

    The brake switch disengages the TCC so it could be the problem. Might check it first to be sure it is seated properly.

  12. #57
    magistrate_apeman is offline Cadillac Owners Member
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    It looks different than any other brake switch I've changed. Surely it's fairly straight forward. For $7 I just ordered a new one. I'll let you know what happens.

  13. #58
    magistrate_apeman is offline Cadillac Owners Member
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    It also seems my doors locks have stopped automatically unlocking when I put the car in park.

  14. #59
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    CadillacLuke24 is offline Cadillac Owners Connoisseur
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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
    It also seems my doors locks have stopped automatically unlocking when I put the car in park.
    That points to your neutral safety switch. Pull your codes, I'd bet you have a P1520.

  15. #60
    magistrate_apeman is offline Cadillac Owners Member
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    Stoplight switch didn't fix it. Darn. But, my lights no longer dim when I apply the brakes. Still no codes.

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