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Please help - surging/stuttering when cold

This is a discussion on Please help - surging/stuttering when cold within the General Help forums, part of the LSx Technical Help Section category; *EDIT* - Looks like there is actually an issue with the ECT circuit to the PCM. I've started another thread ...

  1. #1
    Just another Joe Eagle's Avatar
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    Please help - surging/stuttering when cold - SOLVED

    *EDIT* - Looks like there is actually an issue with the ECT circuit to the PCM. I've started another thread with more details regarding this.

    Long post, sorry... here goes:

    My '02 WS6 M6 has taken to running like crap while its cold. I noticed the problem most obviously while I was watching the car warm up in the morning about a month ago. Upon the first start in the morning, the car's temp gauge fluctuates up and down from dead cold to say 140-160*. The PCM is also obviously seeing this same reading, because the engine idles up and down according to the temp (a bit faster when it reads cold and a bit slower when it reads warm). The needle fluctuates between the two different readings, in about 1 second intervals. So the car sits there and goes, "raaaaaaaaaaah, ruuuuuuuuuuh, raaaaaaaaaaah, ruuuuuuuuuuh, raaaaaaaaaaah, ruuuuuuuuuuh" at idle in the AM until the gauge reads past the first tick mark and then all seems well. When it wants to act real shitty on me, it stutters @ 1-2k RPM for a second or two and then just all the sudden recovers and corrects itself and runs fine suddenly and mysteriously...

    My mileage hasn't suffered, nor has overall performance of the car. The N2O (wet) has been used a few times since this started (after its warmed up obviously) and there has been no problem at all... other than burning up my tires...

    The neighbor is a mechanic who has a basic code reader. I've gotten codes thrown for all sorts of reasons, P0128 (Coolant Temp/Thermostat failure), P0134 (HO2 voltage), P0300 (multi misfire), P0301(misfire cyl1), P0306 (misfire cyl6), P0430(drivers side catalytic failure). Unfortunately, I do not have a tool to read real time data from the car...

    As for the misfires and drivers side cat failure codes - I subsequently found out that I had two spark plug wires that had worked themselves off their coil packs... I fixed that problem and then the misfire codes went away. Both plugs were on the drivers side so I figured I could have toasted the O2 sensor (when pulled it had a whiteish color to it), so thats why it was replaced.

    So far I've replaced: The drivers side pre-cat O2, the temp sender (ECT), and the idle air temp (IAT).

    The temp gauge fluctuating is whats killing me. I can't see how there could be ANY way that the coolant temp is actually changing that much 10 seconds after the car is started in the morning.

    Does anyone know what sensors are involved with calculating the temp that the PCM uses to determine engine speed during warm up?

    I so just want this fixed so I don't have to pull the nitrous out of the car and take it to the stealer (dealer) to fix it under warranty...

    I'll get off the now and hopefully someone can help. Thanks for the read.

    -Eagle
    Last edited by Eagle; 06-18-2007 at 09:23 AM.

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    Just another Joe Eagle's Avatar
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    Oh, additionally, the heated catalyst section of the DTC scanner doesn't seem to ever pass, or it just takes a very long time. Its been probably 300mi since I last cleared the DTCs and it still hasn't passed...

    -Eagle
    | '02 WS6 M6 | KOOKS/ORY | LC-1 | LOU'S SS | UMI SFCs | BMN LCAs & RELOC's | Hotchkis STB | HSW 150 shot | Lid | 42# Lucas | HPTuner Pro |

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    Just another Joe Eagle's Avatar
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    bump. anyone?

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    Just another Joe Eagle's Avatar
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    Nobody?

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    Junior Member chuckstop00's Avatar
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    A general thing to check would be your voltage while running, make sure it's
    not near the low end. I had a bad throttle position sensor, but it did the
    opposite, ran funny when hot. Sorry, not much more . . .

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    Veteran 0rion's Avatar
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    Man, I would think it would be your ECT sensor but you say you've already changed that. I'd have to think on this one a bit. Wonder if you got a bad sensor out of the box?

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    Just another Joe Eagle's Avatar
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    I'm starting to wonder the same thing. I replaced the thermostat and housing last night. Same behavior this morning, so I shut it right back down and followed the troubleshooting process @ gearchatter for the harness itself (connect the 2-wire connector to a 3-amp fused jumper). The car started right up, and idled smooth (no surging and it is cold!) albeit a bit high at just under 1000RPM. The fans both turned on too, but the dash gauge read full cold.

    I'm going to spend another $25 for ANOTHER ECT sensor right now. I'll post up the results in an hour or so.

    -Eagle

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    Just another Joe Eagle's Avatar
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    Bought a 2nd ECT sensor, and just plugged it into the harness with the car cold. It does the same thing. Temp gauge is fluctuating up and down and the RPM is surging. :clueless:

    -Eagle

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    The scanner I have still shows the HTR blinking... its been an easy 400mi since the codes were cleared. No DTCs stored, but that damn HTR part on the scanner still hasn't passed...

    Whats that mean?

  10. #10
    Just another Joe Eagle's Avatar
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    http://www.ls1.com/forums/showthread...522#post825522

    More info on this thread. I'm sure I'll be able to solve this now.

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