High rpm reading.

EBKKB

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Recently noticed my rpm gauge is reading at like 1100 at idle even when warmed up. According to scan tool data (autel) my rpms are at 600 to 800 range. Any ideas as to why my rpms read wrong?
 

melsg5

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Do you have a check engine light on?
Have you checked for a vacuum leak?
If your year and engine is equipped with an IAC valve have you checked it?
 

EBKKB

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Do you have a check engine light on?
Have you checked for a vacuum leak?
If your year and engine is equipped with an IAC valve have you checked it?
Iac has been replaced from a different issue I had. Haven't checked for vacuum leaks yet and the only cel I have is for a p0172 but I don't think it's a vacuum leak because the car runs completely normal. Got an upstream o2 sensor coming in Thursday to hopefully fix that.
 

melsg5

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Iac has been replaced from a different issue I had. Haven't checked for vacuum leaks yet and the only cel I have is for a p0172 but I don't think it's a vacuum leak because the car runs completely normal. Got an upstream o2 sensor coming in Thursday to hopefully fix that.
Doesn't mention O2 sensor.
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EBKKB

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Well good thing they're cheap and mine could need replacing in the near future. I don't know what website I was reading but it mentioned a faulty o2 sensor because that is what relays the info to pop the code. I'll have to go through these causes and double check everything. Any who, I have a picture now of where my rpms idle at.
 

pontiacman1234

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Well good thing they're cheap and mine could need replacing in the near future. I don't know what website I was reading but it mentioned a faulty o2 sensor because that is what relays the info to pop the code. I'll have to go through these causes and double check everything. Any who, I have a picture now of where my rpms idle at.
since your gauge is reporting differently than the computer i would find where its getting its information from. gm gauges are known to wander a bit as they get older so it may be the gauge or the sensor reporting wrong. there should be a spec in resistance somewhere for at least the sensor . as for the running too rich put fuel injector cleaner in it and regap and clean all of your plugs. usually fixes the issue
 

EBKKB

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since your gauge is reporting differently than the computer i would find where its getting its information from. gm gauges are known to wander a bit as they get older so it may be the gauge or the sensor reporting wrong. there should be a spec in resistance somewhere for at least the sensor . as for the running too rich put fuel injector cleaner in it and regap and clean all of your plugs. usually fixes the issue
Which sensor does the pcm use the display rpm readings?
 

melsg5

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Crankshaft position sensor
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EBKKB

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Could be the gauge too. You have no codes indicating a bad sensor.
True. Only code I have at the moment is a p0172. Thinking about hitting a junkyard and seeing if I can nab a cluster and see if it fixes the problem. Might even fix my gas gauge reading a quarter off.
 

EBKKB

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Could be the gauge too. You have no codes indicating a bad sensor.
I was told replacing the stepper motor for the gauges could fix it, what do you think?
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pontiacman1234

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as it turns out the gauge cluster doesnt get its signal from the crank sensor (maybe?) as my pontiacs computer reports engine rpm at 1612 rpm when the engine is idling at 800 rpm so find the sensor or grab a cluster
 
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