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Cadillac Seville / Cadillac Eldorado Forum Discussion, 2003 STS - Rough idle and hesitation on takeoff in Past Cadillac Vehicle Discussion; Put the car up on a lift, let it cool down, grab the heat shield (to preclude that possible rattle) ...
  1. #16
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Put the car up on a lift, let it cool down, grab the heat shield (to preclude that possible rattle) and judiciously thump the converter end pipes with a rubber mallet - Rattles ?

    Time to look at www.easterncatalytic.com and find one of their direct replacement units. Probably from RockAuto.

    The OP never complained of poor acceleration or road performance - a misfire/poor idle characteristic, hesitation, and a rattle.
    98eldo32v likes this.

  2. #17
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    I have clamped the heat shield so I know it is not that. I asked about the cat in my first post because that was my thought but I thought Ranger said the cat would not do that in one the the first posts. I will have to try to get some money together for one. Thanks everyone.

  3. #18
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Quote Originally Posted by Adamhon View Post
    I have clamped the heat shield so I know it is not that. I asked about the cat in my first post because that was my thought but I thought Ranger said the cat would not do that in one the the first posts. I will have to try to get some money together for one. Thanks everyone.

    Post #5
    Quote Originally Posted by Ranger View Post
    You will not get a DTC for a dirty TB, but it can be the cause of a rough idle.

    That said, it sounds like your CAT is on it's way out.

    Based on your DTC's, I'd start by replacing the MAF sensor.


    No

  4. #19
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    That no at the bottom of that post was after you quoted my question of if my cat would cause the problem. It doesn't matter though, I just misunderstood. Thanks for the help.

  5. #20
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Ok, I went to the muffler shop today to have them put on the Eastern catalytic converter I bought, he told me the cat is bad because of the rattling but it is not what is causing the miss (rough idle) and if he puts on the cat it will go bad without finding and fixing the problem of the miss. I reset the SES light about 2 weeks ago and the light has not come back on. I don't know where to go from here other than to take it to a garage, any other ideas?
    Again it seems to run fine other than in idle when it runs rough and has a slight hesitation when you first push the gas but clears up immediately. My gas milage is down quite a bit as well, my car says 10 mpg in town when I typically would be around 14.

  6. #21
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    kaceyseldo is offline Cadillac Owners Fanatic
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    I know I said this already, but I had a 99 Deville that went through 2 cats before someone told me to change the bank 2 02 sensor. It went back to running perfect.

  7. #22
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Kaceyseldo, Did it set off a code?

  8. #23
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    I didn't know how to check codes then. I just felt serious hesitation on cold start up and I took it up to a buddy who said it was the cat. Two replacements later, an ase mech straightened me out.

  9. #24
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Quote Originally Posted by Adamhon View Post
    Ok, I went to the muffler shop today to have them put on the Eastern catalytic converter I bought, he told me the cat is bad because of the rattling but it is not what is causing the miss (rough idle) and if he puts on the cat it will go bad without finding and fixing the problem of the miss. I reset the SES light about 2 weeks ago and the light has not come back on. I don't know where to go from here other than to take it to a garage, any other ideas?
    Again it seems to run fine other than in idle when it runs rough and has a slight hesitation when you first push the gas but clears up immediately. My gas milage is down quite a bit as well, my car says 10 mpg in town when I typically would be around 14.
    Have you checked the plug wires? The insulation on plug wires breaking down can do mysterious things at idle and even at WOT.

  10. #25
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    2kflhr ................Adamhon drives a 2003 STS ........

    2000 and later have no plug wires. It's coil-on-plug: 8 coils in 2 cassettes with short connector boots for each coil-plug. Waste spark disappeared at the end of the 1999 run, and a slew of engine changes came in - mechanical, electrical, electronic. Different engine. Look in my albums - 6 pages of later Northstar stuff.

  11. #26
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    If you haven't changed spark plugs, boots and springs do so.

    I would also check fuel pressure......

  12. #27
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Ok, I am getting some codes again:
    P0300 random misfire
    P0507 high idle
    I changed the sparkplugs (I used the original spec AC Delcos) and liked at the boots and springs, they looked fine.

  13. #28
    98eldo32v's Avatar
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Check fuel pressure.........

  14. #29
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    Have the codes pulled by an auto shop to pin point which exact cylinder is misfiring and replace the coil to it. You should get a P0301, 2, 3 etc..

  15. #30
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    I just noticed today (my wife usually drives this car) that the miss doesn't start until the car is warmed up.

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