Spark Plug Change, Rough Idle

Oughourj · 11-03-2015, 11:18 AM

Hi guys,

Sorry if this subject has been previously covered but it's driving me nuts and I can't seem to find the right solution. I just changed all plugs with new OEM plugs, approx 44k miles which from what I understand is around when they are due. Since then, the idle has been a bit rough, I can feel what seems like a slight misfire when at idle every few seconds. Before changing plugs, my idle was dead-on 700 rpm with AC on, 650 AC off. Now its around 800 and fluctuates between 750 and 850. I did reset adaptations with the COBB tuner since I put the new plugs in. I doubt the car is still adapting because I had previously reset adaptations before doing plugs and it took one or two drives and the car was back to idling normally with the old plugs.

Trying to diagnose the issue but the car isn't throwing any codes and still pulls as it always has WOT through the rev range. I have read that it could be a gapping issue with the plugs but from what I know these plugs are pre-gapped.

Other info: I'm stock with BMW PE, COBB Sport tune. I have ruled out a bad coil because I am not able to pull codes, also ruled out carbon on valves because that wouldn't cause a rough idle out of the blue I feel like it would gradually get worse, though mine's probably due for a cleaning anyway. Also, the rough idle is still present when the engine is fully warmed up.

Some people have told me to put old plugs back in, others to adjust gap on the plugs to what was on the used ones. Any suggestions? Thanks much.

SchismX · 11-03-2015, 03:58 PM

Are you sure you didn't mistakenly get the N55 plugs? Are they the BOSCH ZGR6STE2?

Better yet, are these the ones you installed?

Oughourj · 11-03-2015, 05:12 PM

Yup just double checked, it's the ZGR 6 STE2. Drove it today, it looks like its figuring it out. 700 rpm give or take steady idle when warm, less stumbling at idle than I noticed the last few times. Maybe it really does take a few drives for the computer to figure it out. I'll post with any updates as I know this is a common issue with people changing spark plugs.

As far as re-gapping, what I've learned is that these plugs come pre-gapped by a computer to spec 0.7mm or 0.28" so there's no way to re-gap them as accurate as that.

11-03-2015, 11:18 AM	#1
Oughourj Enlisted Member 9 Rep 43 Posts Drives: 2010 BMW 135i Join Date: Dec 2013 Location: Dallas, TX iTrader: (0)	Spark Plug Change, Rough Idle Hi guys, Sorry if this subject has been previously covered but it's driving me nuts and I can't seem to find the right solution. I just changed all plugs with new OEM plugs, approx 44k miles which from what I understand is around when they are due. Since then, the idle has been a bit rough, I can feel what seems like a slight misfire when at idle every few seconds. Before changing plugs, my idle was dead-on 700 rpm with AC on, 650 AC off. Now its around 800 and fluctuates between 750 and 850. I did reset adaptations with the COBB tuner since I put the new plugs in. I doubt the car is still adapting because I had previously reset adaptations before doing plugs and it took one or two drives and the car was back to idling normally with the old plugs. Trying to diagnose the issue but the car isn't throwing any codes and still pulls as it always has WOT through the rev range. I have read that it could be a gapping issue with the plugs but from what I know these plugs are pre-gapped. Other info: I'm stock with BMW PE, COBB Sport tune. I have ruled out a bad coil because I am not able to pull codes, also ruled out carbon on valves because that wouldn't cause a rough idle out of the blue I feel like it would gradually get worse, though mine's probably due for a cleaning anyway. Also, the rough idle is still present when the engine is fully warmed up. Some people have told me to put old plugs back in, others to adjust gap on the plugs to what was on the used ones. Any suggestions? Thanks much.
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11-03-2015, 03:58 PM	#2
SchismX Private First Class 37 Rep 131 Posts Drives: '10 135i Join Date: Jan 2015 Location: Germany iTrader: (0)	Are you sure you didn't mistakenly get the N55 plugs? Are they the BOSCH ZGR6STE2? Better yet, are these the ones you installed? __________________ BMS DCI // Catless DPs // BMS OCC // BMW PE // ER CP/TiAL BOV // VRSF 7" FMIC // JB4 + MHD // SSR GT1 // Alpina TCU flash
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11-03-2015, 05:12 PM	#3
Oughourj Enlisted Member 9 Rep 43 Posts Drives: 2010 BMW 135i Join Date: Dec 2013 Location: Dallas, TX iTrader: (0)	Yup just double checked, it's the ZGR 6 STE2. Drove it today, it looks like its figuring it out. 700 rpm give or take steady idle when warm, less stumbling at idle than I noticed the last few times. Maybe it really does take a few drives for the computer to figure it out. I'll post with any updates as I know this is a common issue with people changing spark plugs. As far as re-gapping, what I've learned is that these plugs come pre-gapped by a computer to spec 0.7mm or 0.28" so there's no way to re-gap them as accurate as that.
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