Misfire cylinder 2, 3 and 4
 

I had an abnormal condition on my 03 X5 6 cyl with 112k miles on it when all of the sudden I got a service engine warning light and engine abnormal shake. It was going on for a day or so then engine shake disappeared. The service engine light stayed on and I went to my friend to scan the codes where we detected codes 239, 240 and 241-misfire cylinder 2, 3 and 4. The codes got reset and things are back to normal. My friend said it could be the ignition coils or catalytic converter.
Why it happened and disappeared after all? What could be the issue that triggered that event?

70% chances that the coils are going bad... they are about $35 each... keep in mind that you might need to order them...

Thanks. Why 70%? Could it be something else?

happened to me when I bought my X. It was the coils. Now my #6 coil is acting up. But I have heard these have issues with killing the #6 coil for some reason.

of course it can be anything else, from oil flooded plugs to clogged up fuel filter or faulty cat, or even a dead window regulator... well... maybe not the regulator...:D

chances are, the coils... give us more info - what happens when you drive? hard acceleration? going up a hill?... just cruising?...

I just got off the highway before I felt it.
I was going 80-90 on the highway for 10 minutes or so.
It was a smooth ride. When I got off the highway i drove 30-35 on local road and this is when I began feeling engine shake.
But it was the end of the ride cause I got home. An hour or so later I got out and started the engine to see if it is the same. It was shaking and the engine light came on.
Next morning I drove my car for 10 miles or so. The ride was harsh. Engine kept shaking and I shifted the tranny gear using tiptronic because it was shifting hard in D mode.
I parked my car and went with my kid to the dancing event for a few hours. After the event I got back to the car and felt nothing since then. No more shakes or hard shifts. The only thing remained was the engine lite that we turned of after scanning and reseting it off. My friend who owns the auto repair shop said that three cylinders misfire is not a good sign. It could be the catalytic converter also.

3 cyls out of what? you got V8 or the I6? there is no V6 in BMW engine line up... probably the 3.0i...

i suspect, that high voltage from the coil is shorting out to the ground... however, unless the problem is coming back, i am not sure that throwing parts at the problem is a good idea... just look around for the best price for 12131712219... I paid for mine $32.50 delivered, OEM Busch, not OE... still, made in Germany...

Replace the coils. Similar issue but I had replaced the spark plugs, then got a flashing check engine light with those codes while on the throttle. No issues before I replaced the plugs. I replaced the misfiring cylinder coil in question and the next cylinder had issues. Replaced all the coils with the cheap URO brand and no issues for a few thousand miles.

The reason why you car runs better after resetting the SES is that if there are misfires, the computer will turn off the injectors to the cylinders with the misfires. The misfires may be a slight misfire such as a weak spark or a lean condition but after the computer has detect x amount of misfires it will shut off the injector to prevent damage to the cat converter. Once the injectors are turn off that is a big lost in power because the cylinders are basically dead, whereas before they were still contributing power but not as much power.

Your friend is wrong, there is no way that is a cat failing.
Your car has 2 cats, one for cylinder 1, 2, and 3 and a second cat for cylinder 4, 5, and 6.
See you your cylinder 2, 3, and 4 are in both cats and there are 3 other cylinders without problems.

Coil problems are common, but 3 at once is odd...
Did you replace the plugs at 100k?