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Cadillac Seville / Cadillac Eldorado Forum Discussion, 2003 STS - Rough idle and hesitation on takeoff in Past Cadillac Vehicle Discussion; OK - There are a slew of emissions controls that do not function until the engine coolant reaches about 160 ...
  1. #31
    Submariner409's Avatar
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    OK - There are a slew of emissions controls that do not function until the engine coolant reaches about 160 degrees and the powertrain controls shift to closed loop operation.

    O2 sensors begin to be monitored then - along with a lot of other sensors.

    Use this to try and get a feel for where/when this miss becomes apparent. Somewhere between 140 - 160 degrees coolant temp will put the problem in the emissions controls arena.

  2. #32
    drewsdeville is offline Cadillac Owners Master
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Given the history and remaining symptoms/codes, I'd still suspect the maf - even though you've 'cleaned' it. You'd really need a scope to actually verify anything at this point...

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

    The miss starts around 140 degrees, is there any way to check the MAF?

  4. #34
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Look through my albums for MAF pictures. Community tab ^^, Albums, the red Seville. They're a divorced installation, 5-wire, and do not tend to get in the least bit dirty in these particular cars. (1998 and later).

    You already did the butt plug, so removal of the intake ducting is easy. Loosen the 3 band clamps and carefully work the flex end off the throttlebody and off the MAF. Unplug the MAF - carefully checking all 5 wires for integrity - and remove the MAF. Remember the rubber tab/finger orientation. See anything even remotely "dirty there"? Be very judicious in spraying anything to clean it - especially around those 3 tiny heated resistors. If the 3 resistors are properly spot welded (tiny steel wires) to the MAF bridges it's probably OK

    Air filter as new ? Use a new WIX, Delco, Purolator, PartsMaster, FRAM air filter. The cutesy boutique wetted filters are pure unadulterated junk. If you need to oil-soak a filter media to trap dirt, then the filter itself has real problems........ and MAFs HATE oil.

  5. #35
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Okay, I checked over the maf again, the 3 resisters all seemed to be fine. I sprayed dielectric cleaner all over everything really good, cleaned all the connections of the duct work and still had the problem. I took out the air filter for a minute and tried it to see if that did anything, still had the problem. It starts with the miss when the coolant guage gets to the 3rd line, about 165 degrees

  6. #36
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    Re: 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".

    "I cleaned that and reset the SES light, the problem didn't clear up and now I am getting a P0303 code, cylinder 3 misfire".



    "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 mileage is down quite a bit as well, my car says 10 mpg in town when I typically would be around 14".

    Given the fact that you had to replace a converter, at one time it is probably safe to say, extra fuel was being dumped into the converter. That or coolant. So far we haven't heard anything about over heating.

    A steady miss indicates one of three things: a cylinder that isn't firing because of an ignition problem, a cylinder that isn't firing because it is not receiving fuel (multipoint fuel injected engines only), or a cylinder that has lost compression.

    You have changed the ignition components thus far to no avail. You've cleaned the maf sensor to no avail.

    If you're not throwing a code for the mass air flow, it's probably not that.

    NOW, given the fact that you've recently replaced the converter, what does that leave us? By process of elimination thus far you have pretty much taken the ignition system out of the equation. If the vehicle "seems" to have power on acceleration BUT hesitates, you must have some what decent compression..........

    What could possibly be left....FUEL/AND IT'S DELIVERY.

    When you stated that the vehicle hesitates and clears up, that is a dead give away for poor fuel volume or pressure and/or ignition components. You've eliminated the ignition system already.

    Given the fact you had to replace the converter, the fuel pump has probably been getting weaker thus making the pcm "dump" extra fuel to compensate. The extra fuel IF not burned completely ends up in the converter. Eventually heating it up and ruining it. Either clogging it or it eventually breaks apart, as in your case.

    The converter didn't break on it's own. It was physically damaged or internally damaged. Given the fact you have a miss and NO lean codes, you can rule out vacuum leaks.

    There will be no codes for low fuel pressure/volume.

    We aren't that lucky.

    "Ok, I am getting some codes again:
    P0300 random misfire "

    What's common to all cylinders in a random misfire???

    Fuel delivery/pressure and ignition components

  7. #37
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Time for a scanner with real time data so you can see what's going on without guessing. Very well could be a sensor failed in range that won't set a code but may not move when monitored.
    98eldo32v likes this.

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    Re: 2003 STS - Rough idle and hesitation on takeoff

    A scanner would be helpful, yet a test for fuel pressure would take the fuel pump out of the equation also.

    If the pump is delivering the proper amount of pressure and volume, that removes that part of the fuel system.

    Has the fuel regulator been checked?

  9. #39
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Yeah, that ^^^

    Fuel pressure test gauge - rent it from a big parts store. Use the test port - black plastic cap - on the fuel rail.

    Key ON - at least 40 psi. Running - 41 - 47 psi.

    FPR - NO raw gas at the vacuum line/nipple, engine OFF. NO raw gas at the nipple, engine idling.

    (This still smells like something related to the emissions change to closed loop.)

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    Re: 2003 STS - Rough idle and hesitation on takeoff

    This is the 3rd time he was been advised to check the fuel pressure.

  11. #41
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    I've been reading all the replys and my take on it is: A misfire will cause a Cat that isn't in perfect condition to rattle. The reason for the missfire is probably an exhaust valve begining to leak which in its first stages will miss at a slow idle but on fast idle will allow enough compression to fire and smooth out. Fast idle when cold thus the miss.
    You need to do a compression test to be sure.
    Dave

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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Oldstuff,

    How did the catalytic converter break apart in the first place?

    They don't come fractured/ broken new? Something internally (engine function wise) or externally (physical damage) ruined the converter.

    As stated, the vehicle has a hesitation/miss. The ignition system has been pretty much ruled out, UNLESS we have some BAD new parts. We've all at some time unfortunately have experienced that.

    If unburned fuel enters the converter, we can ruin it. If coolant enters the converter, we can ruin it. Thus far coolant isn't an issue.

    The ignition system has been pretty much scrutinized.

    We have the fuel system, and compression left.
    .
    I left the compression alone because the O.P. stated it cleared up upon acceleration.

    Logically, that would leave the fuel system next, but we all know these motors can run with a little compression loss.

    I'd rather the O.P. have to possibly put in a fuel pump and fuel filter than possible head gaskets

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    Re: 2003 STS - Rough idle and hesitation on takeoff

    Bad compression or burnt valves on a Northstar are pretty rare.

  14. #44
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    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

    Quote Originally Posted by 98eldo32v View Post
    Oldstuff,

    How did the catalytic converter break apart in the first place?

    They don't come fractured/ broken new? Something internally (engine function wise) or externally (physical damage) ruined the converter.

    As stated, the vehicle has a hesitation/miss. The ignition system has been pretty much ruled out, UNLESS we have some BAD new parts. We've all at some time unfortunately have experienced that.

    If unburned fuel enters the converter, we can ruin it. If coolant enters the converter, we can ruin it. Thus far coolant isn't an issue.

    The ignition system has been pretty much scrutinized.

    We have the fuel system, and compression left.
    .
    I left the compression alone because the O.P. stated it cleared up upon acceleration.

    Logically, that would leave the fuel system next, but we all know these motors can run with a little compression loss.

    I'd rather the O.P. have to possibly put in a fuel pump and fuel filter than possible head gaskets

  15. #45
    Adamhon is offline Cadillac Owners Member
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    Re: 2003 STS - Rough idle and hesitation on takeoff

    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.

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