[benro2]

Hi guys, first post I think! Been on the forums for a while - they are a wealth of info! Thanks in advance for the help

I've only had my car for a month so I'm unsure of whether this is how the N54 runs or not... so... as the title says - I think my engine is running a bit rough, both at idle and under load and low rpm, say under 1500. I'd call it more of a vibration rather than it running "rough" like it's running on 5 cylinders or something. I can feel it almost all through the steering wheel, however. If I let go of the wheel whilst at idle the car seems to idle pretty smoothly. If I put the transmission in neutral it's *slightly* smoother but I can still feel a slight vibration through the wheel.

The car has done 60,000 k and has a full service history. The previous owner was pretty pedantic so I'm sure it's not from neglect. My previous car ran really smoothly so I could just be noticing this vibration more than I should - but I've always heard that BMW straight 6's are the best in the world - so I'd expect they should run extremely smoothly!

Any ideas? Anyone else experienced this? I've done a fair bit of searching and it seems that all the other threads weren't quite what I'm experiencing. I plan on doing the Alpina B3 transmission flash soon which apparently keeps revs really low in "D", below 1500 by the sounds of it, so I'll possibly be making this problem even worse...

[benro2]

LOL - it looks like I might be being pedantic, judging by the number of replies!

If this helps - last night I put in 20L of E85 together with 100 RON fuel (E10) = roughly 37.5% E85 (I am running a JB4). It does feel like the car runs a little smoother, but it's still not totally smooth!

Anyone?

[Phil325i]

If it's misfiring on one cylinder it will be bad enough to throw a fault code. Get your car scanned for fault codes, then you'll know...

[mlifxs]

my car does something like this. Stopped, if in Drive or Park, with the air off, the revs fall to around 600rpm and I begin to get a very low frequency sound and slight vibration. When I turn the air on, the revs elevate and the vibration goes away.
Recently, I did some rear suspension beefing up (subframe bushing inserts) and to my surprise it reduced the vibration. It's still there, just not as noticeable.
Not saying this will be your cure (nor mine) but since my car has nearly 125k I plan to inspect / re-torque / possibly replace transmission mounts. I will update if that ends up helping.

[benro2]

Originally Posted by Phil325i

If it's misfiring on one cylinder it will be bad enough to throw a fault code. Get your car scanned for fault codes, then you'll know...

Yes, I keep forgetting to do this! It's definitely not misfiring normally as it's not that rough - it's only a very slight vibration. In fact, I did actually have actual misfiring yesterday since I was pushing the car very hard in extreme heat (40C) and was driving up a steep hill right after and started to hear a weird noise. Gradually this noise got louder and the engine got rougher until I could finally tell it was definitely running on 5 cylinders. It was quite obvious when this happened. I'll pull the fault code for this but since I'm JB4 tuned I'm fairly sure I just need new plugs/coils.

Originally Posted by mlifxs

my car does something like this. Stopped, if in Drive or Park, with the air off, the revs fall to around 600rpm and I begin to get a very low frequency sound and slight vibration. When I turn the air on, the revs elevate and the vibration goes away.
Recently, I did some rear suspension beefing up (subframe bushing inserts) and to my surprise it reduced the vibration. It's still there, just not as noticeable.
Not saying this will be your cure (nor mine) but since my car has nearly 125k I plan to inspect / re-torque / possibly replace transmission mounts. I will update if that ends up helping.

My idle appears to be fairly consistent, with/without the A/C at about 650 rpm, whether in N or D. But, good suggestion with the suspension - I didn't think of that. My car only has just over 60k (km) so I would hope I shouldn't need any suspension (maintenance) mods just yet! Will be interesting to see what that does for you though.

Related to my top post, I am beginning to think that perhaps if I were to replace the plugs, this may reduce this vibration? I'll put in a complete new set of plugs because according to the previous owner's service schedule, they've never been changed. However, what about coils? Should I just get a whole new set of coils in or should I just buy a couple and replace as needed? I don't want to spend a whole lot on coils so I was just going to go with the Bosch OEM's. Are there any others out there for roughly $40 each that do a better job than the stockers?

[hankcah]

If your miles are getting up there, then consider calling around to indy shops for walnut valve cleaning. Carbon build up in valves can lead to rough idles and sluggishness overall. But def do the spark plugs and maybe ignition coils first.