2003 STS - Rough idle and hesitation on takeoff
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 2003 STS - Rough idle and hesitation on takeoff in Past Cadillac Vehicle Discussion; I have a 2003 Seville that is running really rough while idling in both park and gear, then hesitates a ...
  1. #1
    Adamhon is offline Cadillac Owners Member
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    2003 STS - Rough idle and hesitation on takeoff

    I have a 2003 Seville that is running really rough while idling in both park and gear, then hesitates a little when I start to accelerate but clears up almost immediately.
    Some history: last winter my catalytic converter was rattling(inside, not the heat shield) but it let up over the summer, with it being cold again it is rattling really bad but I have never had an OBD code for the converter. Earlier this week with all the rattling it started the idle problem.
    I checked the codes and had P0101 MAF sensor performance
    I cleaned that and reset the SES light, the problem didnt clear up and now I am getting a P0303 code, cylinder 3 misfire.
    My question is do you think my catalytic converter is the problem or do I keep chasing codes?

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    kaceyseldo's Avatar
    kaceyseldo is offline Cadillac Owners Fanatic
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    Either that or an o2 sensor. Or throttle body, maybe coil pack?

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

    Shouldn't I be getting OBD codes for those?

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    kaceyseldo's Avatar
    kaceyseldo is offline Cadillac Owners Fanatic
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    Possibly. I'm just saying that these are reasons you could be getting a misfire.

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    Ranger's Avatar
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    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.

    My question is do you think my catalytic converter is the problem
    No

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

    After I cleaned my MAF the code for that went away. I tried cleaning my TB, I put some carb cleaner on a rag, held the butterfly open and wiped all I could. Do I need to do more than that?

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    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

    The TB cleaning usually involves jamming the throttle butterfly wide open, using an object between the gas pedal and front driver's seat skirt to hold WOT. Remove all the intake ducting and use judicious amounts of TB spray, an old toothbrush, and lint free rags to get the bore and butterfly squeaky clean. While you're there, remove the IAC and clean the top hat plunger and bore. ANY air leak in the intake ducting from the air filter adapter spigot to the TB will give a poor idle, mixture codes, and possibly a low speed miss.

    Do this modification (2000 - 2004 Seville) to make your underhood maintenance checks a LOT easier ........... a 2" PVC pipe cap from any hardware store, secured with a suitable band clamp.
    Attached Images

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    Ranger's Avatar
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Quote Originally Posted by Adamhon View Post
    After I cleaned my MAF the code for that went away. I tried cleaning my TB, I put some carb cleaner on a rag, held the butterfly open and wiped all I could. Do I need to do more than that?
    If it was shiny clean it is good. Did you get the throttle plate perimeter and the backside of the throttle plate as well?

    P.S.
    I think there may be a tutorial (maybe with pictures) in Tech Tips.

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

    I did the butt plug mod already. I think I got the throttle plate, front and back, and the bore pretty clean. I replaced the sparkplugs today and am still getting the rough idle, I'm sure they needed replaced anyways, I'm at 140,000 miles. I will try to re clean the throttle body and the IAC.
    I took it for a drive after the sparkplugs and no SES light yet, just the rough idle.

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    stoveguyy is offline Cadillac Owners Connoisseur
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    U checked the plenum for tears?

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    Re: 2003 STS - Rough idle and hesitation on takeoff

    That "SHOULD" set a P0171 & P0174 code.

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

    Ok, I cleaned out the TB as best as I could, cleaned the IAC plunger and bore, and I'm still getting a rough idle. I tried checking the intake ducting, and I sprayed choke cleaner around the plenum and TB to check for leaks(I saw that on post somewhere on this forum). When I first start the car it seems fine, but as soon as it gets warmed up and the RPM's drop you can feel the rough idle. My SES light is not on since I reset after cleaning everything.
    The idle seems to correspond with the rattle in the cat, would that just be my imagination? or do you think the rattling cat might have something to do with it? I just don't know what to try next and right now I don't have the money for a catalytic converter. So any ideas would be appreciated.

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    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

    The rough idle MAY be vibrating the cat heat shield - yours would be nowhere near the first such problem. Can you stick your foot through the firewall and run the car quickly up to 80 - 90 with no problem ? If so, it's not the cat (restricted). If you have the track and tires to do it, your car should pull strongly all the way to fuel cutoff at 130.

    Did you closely check the spark plug boots for carbon tracks inside, and did you use a dab of dielectric spark plug boot grease inside each lower tip ? .......... Your misfire, cylinder 3, may still be your problem.

    I hope the new plugs were AC Delco (DENSO) #41-987 Platinum - nothing else.

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    Ranger's Avatar
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Is the CAT rattling or is it the heat shield?

    EDIT:
    oops, Sub beat me to it.

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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Wow, you have a rattling converter and wonder why you have a rough idle?

    Hmmm, the converter when it was intact looked like a honeycomb. The reason for this was to let the exhaust gasses flow FREELY through the converter.

    NOW, that the converter is rattling/broken, the gasses aren't flowing freely and actually creating excessive backpressure.

    The motor can't breathe, it's choking... creating a rough idle.

    At times it might clear up slightly because when you hit a bump the broken pieces move around just enough to MAYBE allow some more exhaust flow.

    If you have no ignition issues or fuel issues at this time, the problem is the converter.

    Yet, at one time that converter was overheated for it to break apart from raw fuel or coolant entering it. Another possibility it was physically damaged.

    Replace the converter..........

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