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Cold engine rough idle but no problem when warm?
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Silvergecko
New User
Jan 13, 2012, 2:58 AM
Post #1 of 2
(3622 views)
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Cold engine rough idle but no problem when warm?
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Year of vehicle: Aug 2001
Make: BMW
Model: e46 325ci
engine size: 2.5
Mileage:69000
Hello, so basically whats been happening is, when the engine is cold(engine temp pointer on blue) the car starts fine with idle rpm at about 900 rpm and everything is smooth until the choke starts to disengage. As the choke disengages the rpm will start to drop to 500 rpm and the car will shake pretty badly as if I'm driving over some lose pebbles. Then the check engine light will come on(exhaust emission values have deteriorated light -according to book). Once the car has warmed up and I restart the engine, the light will go off but I have noticed a significant drop in MPG over the past week. So what I do these days is, on cold start I manually hold the throttle at 1k rpm till the engine has gone past the blue temp area and everything performs fine but MPG drop still remains. Last September when this problem first started the error code was bank 2 o2 sensor malfunction and the part was changed. Since then I've had no problems till new year and the same error code appeared(light goes off after car is warmed up) so why do you think the o2 sensor is failing so quickly? Should I take out the o2 sensor and clean it? or it is best to have it changed? What worries me is that its only been 4 months or so that a new one has been fitted(the faulty one replaced not all four).
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 13, 2012, 4:08 AM
Post #2 of 2
(3587 views)
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Re: Cold engine rough idle but no problem when warm?
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Wow, where do i start?
You don't have a choke or anything like it.
That light does not mean only "exhaust emission values have deteriorated light"
It does not mean you have a bad 0/2 sensor
You cannot "clean" an o/2 sensor either
The "check engine" light is an indicator for a system that monitors many electronic functions in the system, also called the "malfunction indicator lamp" (MIL). It can come on for any of hundreds of different causes from any of the systems that the computer monitors. Some are very important and can lead to further component or engine damage and some are emissions related not as serious but still a problem and need to be repaired.
Your first step is to have the computer scanned to retrieve the trouble codes that were set when the check engine light came on. Those codes will give you specific information about what the computer saw and will get you pointed in the right direction to find your problem. With a 1996 or newer and some 95 cars and you have an AutoZone or Advanced auto parts in your area, they will read them for free. Once you have these code numbers, we can be a lot more specific about what your problem may be.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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