94 concours rough idle when hot

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Northstar Engines and System Technical Discussion Discussion, 94 concours rough idle when hot in Cadillac Engine Discussion; Hey Guys, lookin for a little help. My problem is after car reaches full operating temperature, and actually a while ...
  1. #1
    Fent is offline Cadillac Owners Member
    Join Date
    Feb 2005

    94 concours rough idle when hot

    Hey Guys, lookin for a little help. My problem is after car reaches full operating temperature, and actually a while after that, assuming car reaches op temp after about 15 min. usually starts after about 25 min. it begins to shudder or miss intermittantly. starts out very slight and becomes gradually quite worse but continues to be intermittant. like from one stop sign to the next, ok, not ok, ect.. went to my local dealership and they diagnosed my 94 concours with a bad ignition module and said 800 bones to fix, i said thats too much ill take it home. took it home and put in a used ignition module and still had identical problem. talked to tech and he said he was just going off of the codes - po23 electronic spark timing (est) signal problem (egr). po25 (ignition control module ) 24x reference low. and po83 crankshaft to ignition module failure. he said he never cleared codes these were history codes. I then entered this web site and began reading. I cleared codes and did a snapshot and got the po25 code again. I suppose the other codes may come back as i just did this last night at the onset of the problem comming back. My best uneducated guess is some elect component taking a little longer to heat up than the motor, sensor or sompin like that. was hoping someone might save me some time and money.as I am in the middle of buying a house
    Thanks for your help,

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  3. #2
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Fort Lauderdale, Florida

    Re: 94 concours rough idle when hot

    Crank sensors...??? They wire directly to the ignition module in the coil pack so that could be an intermittant..

    Coil intermittant?? Did you change the entire coil pack or just the ignition module.??

    Wire routing of the low voltage wires feeding the coil pack/ignition module too near the high voltage ignition wires..?? If an ignition wire is starting to leak it can cause noise on the low voltage wires and/or if the low voltage wires or spark plug wires were rearranged noise may be being introduced into the low voltage lines.

    Plugs and wires possibly??

  4. #3
    Fent is offline Cadillac Owners Member
    Join Date
    Feb 2005
    Thread Starter

    Re: 94 concours rough idle when hot

    Thanks for the response, very much appreciated. I changed the whole coil pack and ignition module 60.00 used for both, beat 500.00 dealership service dept wanted plus 300.00 to install new. which I cant understand cause it took like 15 minutes to change out. anyway it wasnt even the problem. You would think the service dept. would have run some secondary diagnostic tests after reading the codes to attemt to pinpoint the problem but they just went strictly off the onboard computer and tried to bang me with an $800.00 bill. Anyway, I guess I try making sure wires are routed well 1st. if that dont work try some plug wires then a crank sensor. I considered routing of high and low vltage wires and plug wires just from what Ive read on this web sight but thought if they were bad they would be bad at all temps not just when hot. although I guess Ive always known heat is not a friend of electrical. is there a chance this could be thermostat related heating up just enough to cause a problem. one thing I forgot to mention is this all started as soon as we filled the tank with a fresh tank of premium after running regular unleaded for quite a while. I thought maybe we got bad gas since it started at the exact time we filled up from an empty tank. but have already run that tank through, could this possibly be connected? ran perfectly fine on the regular unleaded. anyway I appreciate your time and consideration guess it's time to start attacking the problem in some manner.

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