Car Acting Strange RPM Problems Need Help
12-28-2012, 10:49 AM
#11
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My Ride: Orient blue '05 545i, Sport/Premium Pkg, 6Speed MT, Xenon, Navi, Blue2th, PDC,
If you are waiting for the check engine light to tell you what is wrong with the car – Good Luck with that!
BTW
It would be helpful to know what engine do you have I6 or V8?
You also need to understand the difference between spark plug and ignition coil.
Ignition coil provides high voltage to spark plug to ignite the gas mixture in the cylinder.
If the coil is bad then it won’t provide the voltage and that cylinder will be dead. You will have Check engine light saying misfire on cylinder x.
But if the coil didn’t go bad 100% it will provide lower voltage. The spark will be weaker and you won’t burn the gas mixture 100%. That would cause vibrations and rough idle.
I am suspecting the second scenario on your engine. It works most the time with lower voltage and sometimes it will miss a spark (this is when your check engine came up).
Other problems with rough RPMs can come from vacuum leaks (common on V8 engines) or problems with injectors, broken sensors, etc. If you have a small vacuum leak you won’t get Check engine light, but engine still will be acting strange.
12-28-2012, 08:02 PM
#12
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Hi,
If you are waiting for the check engine light to tell you what is wrong with the car – Good Luck with that!
BTW
It would be helpful to know what engine do you have I6 or V8?
You also need to understand the difference between spark plug and ignition coil.
Ignition coil provides high voltage to spark plug to ignite the gas mixture in the cylinder.
If the coil is bad then it won’t provide the voltage and that cylinder will be dead. You will have Check engine light saying misfire on cylinder x.
But if the coil didn’t go bad 100% it will provide lower voltage. The spark will be weaker and you won’t burn the gas mixture 100%. That would cause vibrations and rough idle.
I am suspecting the second scenario on your engine. It works most the time with lower voltage and sometimes it will miss a spark (this is when your check engine came up).
Other problems with rough RPMs can come from vacuum leaks (common on V8 engines) or problems with injectors, broken sensors, etc. If you have a small vacuum leak you won’t get Check engine light, but engine still will be acting strange.
If you are waiting for the check engine light to tell you what is wrong with the car – Good Luck with that!
BTW
It would be helpful to know what engine do you have I6 or V8?
You also need to understand the difference between spark plug and ignition coil.
Ignition coil provides high voltage to spark plug to ignite the gas mixture in the cylinder.
If the coil is bad then it won’t provide the voltage and that cylinder will be dead. You will have Check engine light saying misfire on cylinder x.
But if the coil didn’t go bad 100% it will provide lower voltage. The spark will be weaker and you won’t burn the gas mixture 100%. That would cause vibrations and rough idle.
I am suspecting the second scenario on your engine. It works most the time with lower voltage and sometimes it will miss a spark (this is when your check engine came up).
Other problems with rough RPMs can come from vacuum leaks (common on V8 engines) or problems with injectors, broken sensors, etc. If you have a small vacuum leak you won’t get Check engine light, but engine still will be acting strange.
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