Yet another weird idle problem (help me out of the rabbit $$ hole)

[romeo_f]

Hello friends, I own a 2008 m3 6 speed 40k miles, and I have a peculiar idling issue Id like to address to you before beginning to throw big money with same results, so after searching and replacing the basic and cheap stuff first (new plugs, primary o2's, and fuel vacuum valve the problem persists.. Here's how it goes: I turn on the engine and it begins its cold start cycle, once it finishes it comes down to normal idling, 650 rpms, timing at +26 purring like a kitten.. After a minute more less of leaving it idling like this idle becomes rough, it goes up to 750 rpms, it pulls timing to 0 running pig rich, it would correct itslef again after a couple of minutes and it goes on and off like this.. If I step a little on the throttle it corrects itself entirely.. so where should I continue throwing money next? ICV? TAs? BTW no codes are shown on my scanner.. Thanks!!

[KawBoy]

I don't think I can help, but mine [2012] has had a steady idle of around 754RPM, since day one. I've never seen it idles at 650RPM. Good luck though.

[KawBoy]

It is actually 784 RPM @ idle.

[spammysammich]

Do some research on fuel breather valves and see if those symptoms match yours.

[romeo_f]

I changed that one man, located right below the plenum same result, my idle does not go up and down in an erratic way like most people say when theirs are failing, mine stays steady but rough.

[RocketyMan]

How do I say this...but what you are describing is normal.

There is an "idle routine" in order to keep the cats hot. This would make sense as the timing going to 0 degrees advanced would cause the engine to effectively work harder and thus create higher exhaust temperature. You "stepping on the throttle" effectively moves out of this idle routine--temporarily. I would imagine there is a "tune" that can effectively disable this feature.

If you were questioning the ignition system, I would've checked the ion-sensing panel in ISTA to VERIFY if your ignition was giving you problems. This is how I found a very persnickety coil that had very intermittent misfire problems--especially when cold.

Since you say you get no codes, I imagine your fuel trims are perfectly fine while driving n such, ya? Get the car up to temperature--oil at 210F or there-abouts. Do you notice the same symptoms with excessive idling? I'm guessing not as much.

Let us know what you find out!

[romeo_f]

Thanks for reply man, it makes sense, I would try to make the reading with the engine completely hot like you say and verify if this routine goes on..

Originally Posted by RocketyMan

How do I say this...but what you are describing is normal.

There is an "idle routine" in order to keep the cats hot. This would make sense as the timing going to 0 degrees advanced would cause the engine to effectively work harder and thus create higher exhaust temperature. You "stepping on the throttle" effectively moves out of this idle routine--temporarily. I would imagine there is a "tune" that can effectively disable this feature.

If you were questioning the ignition system, I would've checked the ion-sensing panel in ISTA to VERIFY if your ignition was giving you problems. This is how I found a very persnickety coil that had very intermittent misfire problems--especially when cold.

Since you say you get no codes, I imagine your fuel trims are perfectly fine while driving n such, ya? Get the car up to temperature--oil at 210F or there-abouts. Do you notice the same symptoms with excessive idling? I'm guessing not as much.

Let us know what you find out!