help diagnosing rough idle - BMW Forum - BimmerWerkz.com
3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

 
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#1 (permalink) Old 05-07-2010, 10:09 PM
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help diagnosing rough idle

1991 325ic. Reved up, heard a mild pop, then rough idle. Sputters like a VW beetle. Pulled a plug, wet oil on threads. Thought: blown valve cover gasket has allowed oil to foul plugs. Replaced valve cover gasket, plugs and wires. Fired her up, same. Rough idle, sputters like a VW.
Bentleys says ignition problems? Coil? Any ideas before I take her to the Dr. Thanks from a newbie DIY.
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#2 (permalink) Old 05-08-2010, 03:17 AM
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The Valve Cover gasket has nothing to do with fouling the plugs. They are separate in all sense of the word. You should be concentrating on looking for any Vaccum leaks, ICV valve, Airflow sensor, or the cap & rotor. Also ensure that all your plugs are getting current and the wires aren't brittle or shot.



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#3 (permalink) Old 05-08-2010, 12:25 PM
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Thanks, I appreciate it.
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#4 (permalink) Old 05-09-2010, 07:32 PM
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Does in have blue smoke coming out the exhaust? Could be a ring. Check plugs, wires, cap and motor.


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#5 (permalink) Old 05-09-2010, 09:09 PM
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No blue smoke. Replaced plugs and wires.
Will check cap and rotor and vacuum issues. Havent check ICV or O2 sensors yet. Will post the solution once I find it to help anyone else who searches the threads.
Thanks.
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#6 (permalink) Old 05-09-2010, 11:49 PM
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Have you thought about the injectors the could be clogged.
Is it miss firing or just idling rough? There is a big difference
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#7 (permalink) Old 05-10-2010, 12:10 PM
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Ya, I guess its more of a misfire. It holds a consistent idle (will not stall) but is running rough, some loss of power (obviously). Sounds like an old VW Beetle. You can hear it sucking air, almost like its whistling and its sputtering, like those old beetles do. Holds a steady idle, just running rough, no matter what rpm. Not backfiring. No smoke.

Had the wet oil on the threads of the old plugs. That was probably the valve cover gasket leaking down to the plug holes. (replaced). Thought maybe the oil caused them to foul, but then again the oil was on the threads not the tip where the plug fires. Someone corrected me on that, Im a newbie DIY.

Old plugs had some carbon, didnt look too bad to me.

Old wires looked ok too, but replaced them anyway. What the heck? They were old, on the care when I bought it 2 years ago.

I think the ICV is ok. It hums and vibrates, turns ok inside, free movement.

Was going to start taking hoses apart thinking a vacuum problem and look at the coil.

Like I said, weird, never done this. Pulled out onto a major road, reved to 3000 rpm, heard a mild pop and then it began misfiring.

Thanks.
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#8 (permalink) Old 05-11-2010, 09:06 PM
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that sounds like a burnt valve buddy... good luck
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#9 (permalink) Old 05-20-2010, 08:29 PM
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Thumbs up how it turned out

Theluis gets the prize for the bad injector advice.

Breathe, thank God. Not a burnt valve!

Vacuum smoke test, OK.
Coil, OK.
Compression, OK, but #4 not firing. Cause, bad injector (original). Replacing them all, doing the valve adjustments. New plugs and wires.

Running like new.

Thank you for your help. This is part of the reason I bought this car. Had a 1980 320i in college with 200K on it running strong when I sold it. I know these cars are tough. The wealth of information for a newbie DIY from other enthusiasts in the community is appreciated.
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#10 (permalink) Old 05-20-2010, 08:48 PM
OMFG another one!?
 
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Glad it's sorted!

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#11 (permalink) Old 05-21-2010, 10:40 AM
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your welcome, 10acity
anytime
glad your car is running like a bimmer should be again!!!
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