Rough Idle After Spark Plug Change - BMW Forum - BimmerWerkz.com
3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.

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#1 (permalink) Old 02-19-2005, 01:58 AM
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Took my 1992 325i sedan to a german mechanic for a valve cover gasket change and spark plug change (oem new plugs which I provided). Valve cover gasket replacement was preventative as it was starting to get greasy on the engine block. Car had no problems whatsoever prior to work.

When I picked up the car the idle was VERY rough. I pointed this out to the mechanic. Don't know how pertainent this is but of note he had mentioned that while initially changing out the plugs some oil had builded up into spark plug housing 2 and 6. This had been cleaned up per the mechanic.
And he said that the rough idle was because some oil may have leaked in the ____ and to drive it off. After a week the rough idle had decreased but is still present.


What is the cause of the rough idle? And what action should I take?
Are plugs not in correctly? The gapping? Do I need new coils?

please advise,
parker1000
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#2 (permalink) Old 02-19-2005, 11:57 AM
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could be that the spark plugs weren't adjust right...


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#3 (permalink) Old 02-19-2005, 12:17 PM
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oem plugs come pregapped. If you use the oem NGK or Bosch, you never gap them. If you didn't have the idle problem before, I would guess that your plugs may not be installed properly. Hard to believe if you took this to a reputable mechanic, but you can find out pretty easily. Go back to him or give him a call, and ask him to what ft/lb he torqued the plugs. SHould be 22lbs per plug. If he studders, or doesn't rattle that info off quickly, that may be your problem. Sounds finicky, but our e36 cars have a pretty finicky electircal system, and depend on everything being installed to relatively exacting specifications. I found this out upon changing my plugs, and doing a little research.

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#4 (permalink) Old 02-19-2005, 12:57 PM
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so pregapped spark plugs (per Jillphan's reply) done by a good mechanic. Maybe it is time to look somewhere else for the causes of rough idling problem? vacuum leaks, MAF, coils etc? A diagnostic tool may have an answer/code with a check engine light soon.

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#5 (permalink) Old 02-19-2005, 04:28 PM
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Torquing the plugs properly is critical. If you remove the plugs and see burn marks around the white portion of the plug, it's definitely that your mechanic did it torque it and tighten it enough.

I don't know the lbs*ft, but the proper spec is 30Nm.

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#6 (permalink) Old 02-19-2005, 07:14 PM
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Thank you all for your reponses. I will make a note of this when I return to have the plug issue resolved. Based on the repsonses it seems likely that the plug installation is the problem.

Of note he did a simple diagnostic test using some computer and it read a fault on my computer. He said that if replacing the plugs don't work he will have to diagnose the problem to make sure that the coils are not shot, computer is not shot, etc. Of note I have no check engine light on.

I HOPE the problem does not get this far and hope that the plugs were not in correctly. But if there is a bigger problem i.e. vacuum leaks, MAF, coils etc as pointed out by billb this problem is BIG as I only went to get a valve cover and spark plugs replaced. Is the next step the BBB? Got to cover all bases and come prepared because I am going back to the shop on tuesday.

regards,
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#7 (permalink) Old 02-19-2005, 07:23 PM
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also it could be that something could ahve dropped into the combustion chamber when he did the profile gasket, its happened before, where someone tried to clean out the oil left over from leak in teh old gasket and with the plugs out anything can fall through. thats an extreme situation and most likely in this case not probable.

it could be a problem with the plugs themselves. what brand did you use? bosch , Beru, NGK?

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#8 (permalink) Old 02-19-2005, 07:33 PM
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The mechanic said initially when the car was idling very roughly that some oil could have leaked through but its been 300miles since the service. While the idle is not as rough as initially it is still very noticeable.

The plugs were new Bosch F 7 LDCR

The mechanic went as far as to say that maybe one or more of the plugs I supplied were bad and recommended that I bring in 6 new plugs. Well I will give him the benefit of the doubt and have him purchase for me 6 new OEM bosch replacements and have him reinstall them.

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#9 (permalink) Old 02-19-2005, 07:35 PM
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hmm F7LDCR are the right ones.

a new set of plugs is what i would recommend too, or at least try your old ones, to see if the idle was the same as it was before. (that is assuming that you never noticed any roughness)

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#10 (permalink) Old 02-19-2005, 07:40 PM
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when he buys you the plugs and installs them if the problem does not get fixedc make sure you do Not pay him one dime. your plugs were fine and the new ones were not needed... dont be mean just dont pay him

David
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#11 (permalink) Old 02-19-2005, 09:41 PM
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Quote:
Originally posted by parker1000@Feb 19 2005, 07:14 PM
Of note he did a simple diagnostic test using some computer and it read a fault on my computer. He said that if replacing the plugs don't work he will have to diagnose the problem to make sure that the coils are not shot, computer is not shot, etc. Of note I have no check engine light on.
regards,
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hmmm, no check engine light? I would say if you had a fault and a poor idle, it could be your O2 sensor. But then you would have a check engine light on.

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#12 (permalink) Old 02-20-2005, 12:19 AM
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Something to think about: When these cars get oil leaking by the valve cover gasket area that is on the inner part of the valve cover, it fills the spark plug wells up with some oil. If that is not removed before you pull the plug, it drops down in. When you fire up the car again, that oil has nothing to do but burn off. This may foul your plug surface. It will definitely send a large white cloud of nasty stuff out your exhaust, which will not clear up until all the oil has burned off. I have been wondering if that has the ability to foul your O2 sensors in the exhaust? This could give you a fault code, and could cause a rough idle. Just a thought.
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#13 (permalink) Old 02-20-2005, 12:39 AM
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something else to think about. Haven't changed plugs yet in my car. But I understand you have to loosen or remove each coil to replace plugs. Could there be something not snapped or put back together correctly?

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#14 (permalink) Old 02-20-2005, 06:44 AM
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Just a thought, if he chnaged the cover gasket he would have had to disconnect vac pipes etc, maybe something hasnt been reconnected correctly or even at all, it only takes a small vac leak to bugger any engines idle up.

Best regards David
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#15 (permalink) Old 02-21-2005, 11:00 PM
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A point brought up by a co-worker I had asked. He said that if they stripped the spark plug housing (which he said can be done quite easily) that would cause an air leak and cause a rough idle.

How true is this statement?
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