car idles like cr*p after replacing si board and 6 button obc.

[gmiller5m]

Get this...I replaced my si board and 6 button obc with good used ones (from a 91 318is) on my 90 325i. I fire it up and it idles like cr*p. Surges between 200 and 500 rpms and stalls. When I'm on the throttle it runs fine. It just can't hold a steady idle when cold or warm. So i switched everything back to the broken cluster and broken 6 button obc and it still idles like cr*p. Would switching out those 2 parts kill the idle? Crazy, I didn't even open the hood. Any ideas?

Thanks.

[OrganicMechanic]

Idle air controller on side of throttle body to boot to intake. Ohm test, carb(on) clean. Could be pulled wire in loom as well.

[gmiller5m]

ran it for 40 miles and then it ran just as good as before. Then i disconnected the battery for an hour and it ran like cr*p again until 30 or so minutes passed. Does the ECU relearn timing advance and such everytime there is a battery disconnect?

[fretburnr]

ran it for 40 miles and then it ran just as good as before. Then i disconnected the battery for an hour and it ran like cr*p again until 30 or so minutes passed. Does the ECU relearn timing advance and such everytime there is a battery disconnect?

yessir. car goes into dumb mode every time you disconnect the battery.

[clavinZERO]

I have undone my battery millions of times, and it has never run THAT shitty afterwards. It sounds like something else is up.

[gmiller5m]

yeah. its pretty crazy, my land rover isn't even this moody. When it idles poorly i can turn on the A/C and the idle smooths out immediately. Turn off the A/C and starts surging up and down.

[jlevie]

ICV, an intake leak, or aged O2 sensor would be the most likely causes.

[thereisnoyun]

ICV, an intake leak, or aged O2 sensor would be the most likely causes.

I concur, it would seem like the comp adjusted to whatever faulty part after you drive it a while. o2 would be my first guess.

[gmiller5m]

this happened when it was cold and the o2 sensor has less then a month on it. Thinking it was a vacumn leak too, I sprayed carb cleaner around the engine to see if it increased the idle when it was surging without any luck. The ICV is always a suspect but i hesitant because after that initial 30min. computer retune there isn't any surge/hesitation in the idle or while driving at all. I'm going to change out the engine temp sensor and the coolant temp sensor and see if that has any affect. My thinking is that is one of thoes is bad it might cause the rich/lean surge as its trying to map actual spark advance with an incorrect engine temperature. But please let me know if I'm completely off base...