93 38 service engine Light on.... RPM up and down - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-18-2006, 02:50 PM   #1
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Default 93 38 service engine Light on.... RPM up and down

Hi
1993 Bonneville 3.8
My wife was driving the other day and the service engine light soon came on. All gauges and fluids were fine but then she said the rpm went up and down a bit on their own??? The the light went off for a day now its back on .Runs a bit rough but always has.. Appreciate any ideas on what to check.
Mike
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Old 03-18-2006, 02:56 PM   #2
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When stopped, does the RPM'* go up and down? How does the car run when driving?

Sounds like it could be an Idle Air Control sensor. You need to get the code to pinpoint your problem.
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Old 03-18-2006, 02:56 PM   #3
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Old 03-18-2006, 03:50 PM   #4
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After talking to the wife in more detail she says the rpm gauge is being erratic not the rpms. This occurs while going down the hwy?? Light is still on. I will check the codes.
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Old 03-18-2006, 08:33 PM   #5
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Thanks guys.
After the wife Got home I took it for a drive the rpm gauge is acting jumpy but the motor seems to be running normally. The check engine light soon is still on so I checked the codes and got 4 flashes then a pause then 2 more flashes it did that 3 times. What does this mean??
Appreciated
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Old 03-18-2006, 08:43 PM   #6
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A code 42 Electronic Spark Timing Circuit. I don't know what to look for. Someone else can help.
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Old 03-18-2006, 10:11 PM   #7
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Could be the crank sensor or ICM. I'd have to dig deeper, but I refuse to burn dinner.
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Old 03-18-2006, 11:02 PM   #8
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Crank sensor sounds serious what is ICM? Please let me know?? Car is not running any different?
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Old 03-19-2006, 12:18 AM   #9
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Ignition control module, three coils sit on top of it where your spak plugs lead to.
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Old 03-19-2006, 01:17 PM   #10
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Thanks
But wouldn't the car run like @#$% if the ICM was bad??? It runs a bit rough but always has?? How would I know if it was either of these problems for sure??
Appreciated
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