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Cadillac Seville / Cadillac Eldorado Forum Discussion, 2003 STS - Rough idle and hesitation on takeoff in Past Cadillac Vehicle Discussion; That rip in the plenum is always at 6:00 and a lot of times you have to flex the plenum ...
  1. #46
    Ranger's Avatar
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    That rip in the plenum is always at 6:00 and a lot of times you have to flex the plenum to open it up while spraying. What really surprises me is that you didn't get A P0171 & P0174 code.

  2. #47
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Something isn't right here in Denmark........

    "Do you suppose that a miss at idle caused by low compression might over fuel the Cat and cause failure? When the engine is missing (not from lack of fuel) the unburnt fuel has to go somewhere".
    Dave

    Dave, I agree that CAN happen BUT,

    Even IF that was the case, FIRST without a doubt, the check engine light be will be on. It would be FLASHING to get your attention to a severe emissions malfunction.

    Second, at this particular moment the car went from one particular cylinder misfiring to a random cylinder misfire. One cylinder had a possible issue, but now all cylinders are being affected. Therefore there is a issue affecting all cylinders.

    "Okay, I just got back from the mechanic, I have a tear or hole in the plenum? I tried spraying carb cleaner all over that with it running but evidently I didn't get it in the right place, he took a can of brake cleaner and sprayed right on it and the rpm's went right up".

    I don't know what's going on, but everyone that has been around these northstars long enough to know a plenum tear causes lean codes P0171 and P0174 that the O.P. has NEVER stated up to now........

    I'll sit back and enjoy the show now........

    This should be interesting.

  3. #48
    oldstuff is offline Cadillac Owners Fanatic
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    True but if the Cat was bad wouldn't that also be the case? Imbalance in O2 sensor readings from front to rear of the convertor. So a plenum leak would cause the miss but not a Cat failure as it would be a lean idle problem. The computer would then increase the fuel supply to compensate and could be responsable for the random miss. The over rich mixture wouldn't cause a build up of fuel in the cat like a miss dumping raw fuel into it.
    Just kicking ideas around, there are a lot of varriables.
    Dave


    I didn't say a valve was the only reason but it was a possibility'
    Dave

    Quote Originally Posted by 98eldo32v View Post
    Something isn't right here in Denmark........

    "Do you suppose that a miss at idle caused by low compression might over fuel the Cat and cause failure? When the engine is missing (not from lack of fuel) the unburnt fuel has to go somewhere".
    Dave

    Dave, I agree that CAN happen BUT,

    Even IF that was the case, FIRST without a doubt, the check engine light be will be on. It would be FLASHING to get your attention to a severe emissions malfunction.

    Second, at this particular moment the car went from one particular cylinder misfiring to a random cylinder misfire. One cylinder had a possible issue, but now all cylinders are being affected. Therefore there is a issue affecting all cylinders.

    "Okay, I just got back from the mechanic, I have a tear or hole in the plenum? I tried spraying carb cleaner all over that with it running but evidently I didn't get it in the right place, he took a can of brake cleaner and sprayed right on it and the rpm's went right up".

    I don't know what's going on, but everyone that has been around these northstars long enough to know a plenum tear causes lean codes P0171 and P0174 that the O.P. has NEVER stated up to now........

    I'll sit back and enjoy the show now........

    This should be interesting.

  4. #49
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Dave,

    I completely agree.

    I feel at the present time, we aren't getting the full picture of the issues.

    Misfires over an extended period of time and or any emissions malfunctions probably will affect catalytic converter longevity in the long run.

    At this point I hope he can solve the problem inexpensively, whatever it maybe.

  5. #50
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Adamhon, For insight on the plenum angle ............ many pictures/diagrams in my albums. The Community tab, the red Seville. 2 albums, 6 pages of stuff for your engine/car.

    You can barely see the plenum and band clamp screw - remove the engine cover, flashlight - down in the area between the throttlebody and intake manifold. The black rubber/steel connector bellows.

    A 2 hour fix with decent hand tools and a bit of wrenching experience.

    The air leak is just large enough to affect driveability - when the mixture controls change from rich to lean at open loop.

  6. #51
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Changed the plenum and the catalytic converter, still having the problem and getting the random misfire and high idle codes.
    I'll have it back out at the mechanic to put on the computer and give you all an update, hopefully I can get it in tomorrow but we are supposed to get 6-10 inches of snow so we see.
    On a side note, the Eastern cat has a rumble to it, quite a bit louder than the original, I'd love it on a Camaro but don't care for it on a Caddy.

  7. #52
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Hot dawg !!!! (You're not driving a mushmobile "Caddy" - it's a F55 STS !)

    Eastern direct fit cat - perfect companion for my CORSA system.

  8. #53
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    Re: 2003 STS - Rough idle and hesitation on takeoff


  9. #54
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Haven't had a chance to get the Caddy on a computer, its been freezing here and my mechanic can't heat up his garage enough. I have noticed every time I work on it, wither the time I cleaned the MAF, or the time I cleaned throttle body, or the time the plenum was replaced; it seems to do a little better(doesn't seem to have problems till almost 160 degrees, the rough idle is not as hard) but after a couple times driving it gets worse(problem starts around 140 degrees, rough idle is really noticeable). Does that give anyone some ideas?

  10. #55
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    I won't re-type Post #31 again.

  11. #56
    power007 is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Quote Originally Posted by Submariner409 View Post
    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.
    What's the reason for remove the air intake resonator

  12. #57
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    Makes transmission fluid level checks and air filter changes much easier.

  13. #58
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    The mechanic said it has a misfire on cylinders 3 and 4, he said he would replaced the back coil pack and see if the fixes both because a misfire in one cylinder can affect another.

  14. #59
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    #3 is on the right bank, #4 is on the left. Your car does not have waste spark ignition, so one coil does NOT fire two plugs at the same time - that went out with the start of the 2000 model year (08/99).

    Your firing order is 1-2-7-3-4-5-6-8 ........... maybe he's trying to tie that firing order to a miss condition. Not likely.

    ............. and a 3-4 miss would cause VERY noticeable driveability problems - that's 25% of cylinders not firing in sequence - huge 180 degree dead spot in crank rotation.

  15. #60
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    So you think I need to change both coils?

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