temporary "service engine soon" + rough idle

[XAMI]

First time it happened a week ago, i was merging onto the highway with overdrive-on, (no redlining), "service engine soon" came on, I put it into regular drive and the SES light went off after a few minutes.

Yesterday, was in overdrive for a half-block, "service engine soon" came on, I put it back in regular mode and it idled really really rough, I slowly drove home and after a few minutes the SES light was off again.

Any ideas?
08 135i, completely stock...

Thanks

[Huecifer]

engine misfire. Spark plugs are going bad. Fix them soon before they take the coil packs and injectors with them!

[jaye944]

MOST common culprit is coil pack, misfire then causes the spark plug to foul.

Get a scan of the error codes it will tell you

Originally Posted by IAMX

First time it happened a week ago, i was merging onto the highway with overdrive-on, (no redlining), "service engine soon" came on, I put it into regular drive and the SES light went off after a few minutes.

Yesterday, was in overdrive for a half-block, "service engine soon" came on, I put it back in regular mode and it idled really really rough, I slowly drove home and after a few minutes the SES light was off again.

Any ideas?
08 135i, completely stock...

Thanks

[ShocknAwe]

+1 on reading the code. Will tell you what cylinder it is. Easy to swap the coil across cylinders to check if it's the coil or plug.

I'm sure the injectors are fine.

[XAMI]

Question, since the check engine light only came on for a little bit when it was in limp mode, when i finally took it to autozone to have them read the code, they didn't see anything. Do i need to find someone with a better reader to read the past codes? Or do I need to reproduce the problem to make the CEL come back on and have it read at that point? thanks

[1mang]

Not all code readers are the same. You might want to try another one.

A hard CEL (light on) is easier to read than a soft/hidden CEL (light not on).

[dm874]

How many miles are on the car? Changing spark plugs is always a good idea as preventative maintenance. I feel like the spark plugs are the issue because a bad coil would usually shut off a cylinder and it wouldn't clear the code until after shutting off the car.

[XAMI]

Originally Posted by dm874

How many miles are on the car? Changing spark plugs is always a good idea as preventative maintenance. I feel like the spark plugs are the issue because a bad coil would usually shut off a cylinder and it wouldn't clear the code until after shutting off the car.

It has about 57k,
I tried the overdrive a few more times recently (gently) and no problems or code popping up,

I bought spark plug socket in case I need it soon,

[Jeb_]

Had a similar thing happen to me when I was test driving an '11 128i a couple weeks ago. The test drive went great but as I was one stop light away from getting back to the dealership and buying the car it started misfiring and the service engine light came on. Needless to say I didn't leave in a 128i that day.

It probably was something simple like the plugs but I'm not about to take the chance.

[Dackelone]

Originally Posted by IAMX

Question, since the check engine light only came on for a little bit when it was in limp mode, when i finally took it to autozone to have them read the code, they didn't see anything. Do i need to find someone with a better reader to read the past codes? Or do I need to reproduce the problem to make the CEL come back on and have it read at that point? thanks

That's why they call them "shadow codes" bc only a BMW scan tool can read them. The generic code readers can only read the (generic)OBDII mandated codes. But the BMW tool can read all the various codes. As long as you have not driven the car too long after throwing a SES code... then your dealer should be able to read the code either from the key fob or from the car itself. But I think after say 100 engine starts or 120 miles... those shadow codes will self erase IF its not a continuing problem.

[ShocknAwe]

Originally Posted by Dackelone

That's why they call them "shadow codes" bc only a BMW scan tool can read them. The generic code readers can only read the (generic)OBDII mandated codes. But the BMW tool can read all the various codes. As long as you have not driven the car too long after throwing a SES code... then your dealer should be able to read the code either from the key fob or from the car itself. But I think after say 100 engine starts or 120 miles... those shadow codes will self erase IF its not a continuing problem.

Another one of the many perks of having a JB4. Full code reading & clearing & diagnostic adaptation resets. Automatic battery registration is about to be a thing too!

[jaye944]

YES

Originally Posted by IAMX

Question, since the check engine light only came on for a little bit when it was in limp mode, when i finally took it to autozone to have them read the code, they didn't see anything. Do i need to find someone with a better reader to read the past codes? Or do I need to reproduce the problem to make the CEL come back on and have it read at that point? thanks

[Eg135i]

My car was doing the same thing but then the service engine light came on and it stayed on 3rd gear. Anyone know if it can just be transmission fluid or I need to replace the whole thing? I have an automatic btw

[XAMI]

Turned out to be a cylinder #6 misfire, replaced the spark plugs, and now all is well! thanks for the advice.

[Shaymer]

Originally Posted by IAMX

Turned out to be a cylinder #6 misfire, replaced the spark plugs, and now all is well! thanks for the advice.

Just posted about this. I'll try it. Thanks.