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I have a auto BMW 330i 2010 UK; The car has not been serviced for almost 2 years (I will be getting it done this week. It was due service when I brought it, and then just never got round to it tbh). Car ran fine until last week where I started the car and it had a slightly rough idle. Usually sits at 600rpm, but bounced very slightly upto about 800 and back. Nothing significantly rough, but noticeable. Then the engine light came on. I switched it off, revved up a bit and went on my journey completely fine without any roughness or hesitation from the car.

Yesterday, I had the same issue but while I was driving (maybe 25 mins into my drive), the car sounded really rough and had the typical symptoms of a bad spark plug(s). I pulled over, turned it off and back on, lo and behold it ran fine and the engine light disappeared.

I suspect it is just the spark plugs and getting all 6 replaced this week, but curious as to if it could be anything more mischievous? I've never had a problem like this before, so unsure exactly. No codes are being given off

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  • Did you read the code(s)? This will surely point you in the direction you need to look at ... most codes will linger in the computer even when the dash light shuts off.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 19, 2020 at 16:09
  • @Pᴀᴜʟsᴛᴇʀ2 Apologies I have a very basic code reader which turns out, barely reads anything. Initially I was getting no codes and had to visit a garage to get the codes. Answer is below if you're curious.
    – Nouman
    Nov 13, 2020 at 18:55

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So it turned out not to be so complicated after all but a rather extensive investigative process. I can't for certain say it was this ONE thing that caused the problem, but rather a combination! It was due a service, so I did athe full service with premium parts expecting that maybe the old spark plugs might have been causing the issue. However, the issue was not resolved.

I was getting a misfire on cylinder 4 and 6. Turns out, the mechanics saw oil in the spark plugs and I had a look, and realised the valve cover gasket was leaking. Not substantial enough for the car to be leaking, but there was very visible sludge around the gasket. Had that replaced. I was also getting a MAF sensor error. So I bought some electrical cleaner spray, and cleaned the sensor. Upon re-installation the error disappeared.

Now the code was a misfire on cylinder 1 with no other errors. Simple coil swap to cylinder 2 resulting a cylinder 2 code meant a ignition coil change. And finally, the car is back to normal! It's hard to say which one it was exactly that caused the initial problem or maybe it was everything. If you're having a similar issue, I would start with the cheaper options. Start with plugs unless they've been changed, then coil pack. Look for oily gasket if you suspect that is the problem. And for the MAF sensor, that's a really easy fix with a dozen YouTube videos.

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