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Thread: why does my engine run rough when its cold?

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    Senior Member 92buick_century's Avatar
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    Default why does my engine run rough when its cold?

    when i start my car when the engines cold, it runs rough, it shakes my whole dash and the engine shakes alot, but when its warmed up it runs smoother, the other day it was running (cold) and just all of a sudden it ran smoother, almost like a valve opened or something, ive tried going around the engine and checking for vacuum leaks, but couldnt find any, ive put injector cleaner in, cleaned the MAF, IAC, and TPS? not sure if thats what it was or not, and nothing has changed, does anyone know what the cause could be? also sometimes when im driving, if i slow down to almost a stop then push the gas and make it downshift, it hesitates/lags, almost acts like its carburated or something, it does it at random times
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!



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    Senior Member Zaloryan's Avatar
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    Check your PCV valve underneath the alternator. Sometimes they'll get stuck shut over time.

    Do you have a cluster with an engine temperature gauge? It's possible that your coolant temperature sensor is bad, telling the ECM to randomly switch between Open Loop & Closed Loop.
    What is this & what does pulling it out do?

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    Senior Member luthoro's Avatar
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    Quote Originally Posted by Zaloryan View Post
    It's possible that your coolant temperature sensor is bad, telling the ECM to randomly switch between Open Loop & Closed Loop.
    That would be my assessment as well. Especially if the change from rough to smooth running was instant, like flipping a switch. Sounds like an electronic thing to me. The second problem might be unrelated.
    -Brendan

    1991 Buick Century wagon LG7/4T60- daily driver, UV front sway bar. On its 3rd life. Refurbishing, work in slow progress. Will get some mods down the road.
    1985 Ford F250 Explorer 460/4bbl- hibernating in a barn since 2005, hopefully will be waking her up soon.

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    Senior Member 92buick_century's Avatar
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    Quote Originally Posted by Zaloryan View Post
    Check your PCV valve underneath the alternator. Sometimes they'll get stuck shut over time.

    Do you have a cluster with an engine temperature gauge? It's possible that your coolant temperature sensor is bad, telling the ECM to randomly switch between Open Loop & Closed Loop.
    i changed my cluster to the one with the volts gauge and temp gauge, but i need to change the sensor so the gauge will work because the sensor now is for the indicator, ill check the pcv valve tomorrow
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!

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    Senior Member jeffreyclay's Avatar
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    I had a mechanic relate a similar story to me. He found that the coolant temp sender was misleading the ECM by showing a hot engine when it was cold from sitting over night. The fuel circuit wasn't compensating for the cold condition (Similar to no choke applied to richen mixture) A good code reader would help you see the reported data.

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    Senior Member 92buick_century's Avatar
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    ok so i took my pcv valve out today, its the original one, im going to replace it, but it still rattles and isnt stuck, so i cleaned it with carb cleaner and put it back in, made no difference. so is it probably the temp sensor? i am going to change it either way so i can make my gauge work
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!

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    Senior Member Zaloryan's Avatar
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    Since you have the 3300 & you just got to the PCV valve, installing the temperature gauge sensor will be easy.

    Computer Coolant Temperature Sensor: Borg Warner #WT3000 (Two wire pin connection)
    Gauge Temperature Sender: Borg Warner #WT3002 (One wire connection)

    The connector for the Gauge Sender will be hidden in the wire loom running right by the alternator. It's a green wire with a very bizarre connector.



    The coolant temperature sensor is entirely independent of the gauge on your dash. All it does is send voltage to the ECM. I'm betting that WT3000 is your problem. There will be a threaded plug adjacent to WT3000 where WT3002 sits. I removed it with a 3/8" extension with no socket.
    What is this & what does pulling it out do?

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    Senior Member 92buick_century's Avatar
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    since my car originally had just the idiot light for the temp, will it still have that wire for WT3002 in the harness? and do i need to replace the original sensor as well as put the sensor for the gauge? also if i take that sensor and plug out will coolant come out of the holes?
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!

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    Senior Member Zaloryan's Avatar
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    "Yes" for all questions, 92 buick century.
    What is this & what does pulling it out do?

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    Senior Member 92buick_century's Avatar
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    ok so do i have to drain the coolant, or can i just take some out?
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!

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    Senior Member Zaloryan's Avatar
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    That's up to you, really. This area is near the top of the cooling system so it won't leak a lot, but it will be a good bit.
    What is this & what does pulling it out do?

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    Senior Member 92buick_century's Avatar
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    the plug for the WT3002, is that the only green wire up there? or is there more then one?
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!

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    Senior Member luthoro's Avatar
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    Nice diagram, Zaloryan. I plan to get the better cluster so that'll help me too.
    -Brendan

    1991 Buick Century wagon LG7/4T60- daily driver, UV front sway bar. On its 3rd life. Refurbishing, work in slow progress. Will get some mods down the road.
    1985 Ford F250 Explorer 460/4bbl- hibernating in a barn since 2005, hopefully will be waking her up soon.

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    Senior Member Zaloryan's Avatar
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    Thanks Luthoro, I like to help as much as I can. Vagueness isn't much assistance, lol!

    92 Buick Century, that's the only (dark) green wire. It should be the only free plug.
    What is this & what does pulling it out do?

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    Senior Member 92buick_century's Avatar
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    ok, when i checked the pcv valve the other day, i found a green wire that was free, the plug was rectangle, but it either has oil in it or the plug is burnt/melted, i didnt really look at it that good

    and ya i agree with Luthoro, thanks for the diagram and the help
    -Devin

    Current car- 88 Olds Toronado Trofeo 3.8L LN3 83k

    Former car- 92 Buick Century Custom 3.3L LG7 151k-SOLD!

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