2003 Rough Idle / Stall
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 2003 Rough Idle / Stall in Past Cadillac Vehicle Discussion; I have a 2003 Deville (130,000 mi) with a P0300 Random Misfire code and a P0410 code. I have replaced ...
  1. #1
    Matt R. is offline Cadillac Owners Member
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    2003 Rough Idle / Stall

    I have a 2003 Deville (130,000 mi) with a P0300 Random Misfire code and a P0410 code. I have replaced the plugs, boots and both coil packs. I cannot find a vacuum leak. Can the Crankshaft Position Sensors fail and not set a code? The car has a serious rough idle, almost stalls after it comes off of high idle. Bad smell from the exhaust as well. Ideas?


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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 2003 Rough Idle / Stall

    Quote Originally Posted by Matt R. View Post
    Can the Crankshaft Position Sensors fail and not set a code?
    Absolutely AND rather common. Been there, done that.

  4. #3
    Matt R. is offline Cadillac Owners Member
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    SmileRe: 2003 Rough Idle / Stall

    I figured it out. Vacuum leak at the back of the plenum..

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    basscatt's Avatar
    basscatt is online now Cadillac Owners 10000+ Posts
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    Re: 2003 Rough Idle / Stall

    Quote Originally Posted by Matt R. View Post
    I figured it out. Vacuum leak at the back of the plenum..
    ----------------------

    also check the FPR - Fuel Pressure Regulator vacuum supply hose -
    it SHOULD be absolutely dry -
    if there is ANY sign of gas in it -
    the FPR diaphragm has a leak -
    and gas is being sucked into the motor -

  7. #5
    Matt R. is offline Cadillac Owners Member
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    Re: 2003 Rough Idle / Stall

    Thanks. I'll check that as well. I'm getting a p0300 code again and I smell gas at start up. Idle is horrible at start up.

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    Re: 2003 Rough Idle / Stall

    If you smell gas, the FPR is highly suspect.

  9. #7
    Matt R. is offline Cadillac Owners Member
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    Re: 2003 Rough Idle / Stall

    Fpr is dry...

  10. #8
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    Re: 2003 Rough Idle / Stall

    Quote Originally Posted by Matt R. View Post
    Thanks. I'll check that as well. I'm getting a p0300 code again and I smell gas at start up. Idle is horrible at start up.
    ==========================
    P0300 is a generic misfire code -
    our on-board code readers will not display WHICH cylinder/cylinders is/are misfiring -
    only that there IS a misfire -

    take the car to any large auto parts store - they will check your codes for free -

    P0301 is a misfire in cylinder #1 - P0302 is cylinder #2 - P0303 is #3 - etc -

    once you discover WHICH cylinder is misfiring - diagnosis becomes much easier -

  11. #9
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    Re: 2003 Rough Idle / Stall

    Quote Originally Posted by Matt R. View Post
    Fpr is dry...
    You did check it with the engine running, didn't you?

  12. #10
    Matt R. is offline Cadillac Owners Member
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    Re: 2003 Rough Idle / Stall

    Yes. I let it run for a few minutes and then pulled the vacuum line off. I have a coil cassette at home, that may be my next step. I had a misfire 302 code last week..

  13. #11
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    Re: 2003 Rough Idle / Stall

    The gas smell is worrisome. If you smell gas, there is a leak and that should be priority #1. Worry about the misfire later.

  14. #12
    Matt R. is offline Cadillac Owners Member
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    Re: 2003 Rough Idle / Stall

    Looks like there is a cylinder head kit in my future. The smell must have been a combination of unburned fuel and coolant. She tried to overheat last night on the way home.

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    Re: 2003 Rough Idle / Stall

    I would not jump to that conclusion on an '03.
    Check the purge line, WP belt tensioner, coolant level and then do a block test if necessary.

  16. #14
    Matt R. is offline Cadillac Owners Member
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    Re: 2003 Rough Idle / Stall

    Coolant in the cylinder explains the rough idle on start up. After a few minutes, it would idle fine. I'll check the items you listed as well, just to be sure. It has 136k on the odometer.

  17. #15
    Ranger's Avatar
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    Re: 2003 Rough Idle / Stall

    Coolant in the cylinder is a death certificate, but I don't recall you mentioning that before.

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