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Discussion Starter · #1 ·
Hey folks! I have recently done quite a bit of work on my engine and got it all put back together! Now, I've come across this idle problem that I can not diagnose and have tried to research it to no avail. My hope is that someone has come across this issue before or will be able to help me identify the issue! When engine is cold will run perfectly for a solid 20 - 30 seconds before idle issue. Here is a list of all that I have touch/fixed/replaced:

NOTE: All were torqued and cleaned before reinstall

  • VANOS(seals/rattle kit/filter/oil line) Did not replace solenoid
  • Injectors (cleaned/tested/new o-rings)
  • Vacuum tube(aluminum) cleaned and replaced 12 o-rings
  • Rod bearings/bolts
  • ITB's were removed and cleaned (did not take of rod)
  • ICV cleaned
  • Coils and plugs (are about 2 years old ~10k miles)
  • Compressions test (all cylinders around 150psi)
  • Smoke test (no leaks detected)
  • TPS front and back replaced (reset)

I am currently running Velocity Stacks and had no issue with idle prior to work.

Here is a video of sound:

I appreciate the help!
 

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When engine is cold will run perfectly for a solid 20 - 30 seconds before idle issue.
It ran smooth from cold engine to about 30 sec because there was no closed-loop control with the O2 sensors feedback. Once the DME closed the loop using signals form O2 then it got in rough oscillation mode due to wrong signal.
* check if O2 cable mixed up
*disconnect the MAF connector and see if it gets smoother.
* check the ICV connection.
 

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Discussion Starter · #3 ·
It ran smooth from cold engine to about 30 sec because there was no closed-loop control with the O2 sensors feedback. Once the DME closed the loop using signals form O2 then it got in rough oscillation mode due to wrong signal.
* check if O2 cable mixed up
*disconnect the MAF connector and see if it gets smoother.
* check the ICV connection.
Interesting. Makes sense too. I've made some modifications to my lil DIY smoke tester and going to have the wife help me out to see if i'm missing anything, so i'll have to give it a couple of hours so I can check that again.

For the MAF connector it is connected to a IAT for the Velocity stacks I have and I may have to check the wiring. Don't think there should be an issue with the actual component for it is a year old-ish and there was no prior issue. I will check after my smoke check.

The ICV connector looks fine with no corrosion as well. Not really sure how to check the ICV itself other than shaking it and seeing it clean.

For the O2 sensors, i've never actually replaced them for the 6 years I've owned the car. I've put about 25k miles on it for the time i've owned and the previous owner(single owner) was very good about making sure it was always updated and good to go. I currently have Catless headers so I should only have to worry about the Pre-cat O2 correct? Since the tune I have should have eliminated the Post-cat O2's. I'm not savvy on the tuning aspect and the current one was over Email and not actually taken in. I was planning to take it in to get it properly tuned after everything is said and done.

I greatly appreciate the response and I will give these test tomorrow with an update!
 

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Discussion Starter · #5 ·
Give us some history. Did this problem just popped out recently, or it was worked on and then the issue appeared?
There was no idle issue prior to maint I have done. I have finally got around to finishing up all the new/rework maint and this is what I have come across. Everything I have described is what has been done to it.
 

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Discussion Starter · #6 ·
Do note though, I did have a tune flashed so it would work with the catless headers and the velocity stacks I have installed. It was a basic tune for Alpha-N so there was no issue just not tuned to spec for my M3.
 

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Discussion Starter · #7 ·
UPDATE! So I had the wife help me out to double check on smoke test and can confirm there is no leaks.

I ran another cold start test with the IAT/MAF sensor disconnected and it did run longer before running into its issue. Of course though, I did get the P0113 code. Then I cleared/cleaned IAT and reconnected and ran it again. This time only taking about 10 secs sitting at ~900rpm before bounce. Code P0113 did come up again. Quite possibly the sensor?

I did have INPA running while this was going on:

NOTE: Injection time did bounce from ~1.50 to ~2.1 while the bounce was going on, which I can only assume is normal.
 

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There was no idle issue prior to maint I have done.
Then it's easy to fix this new problem due to a bad connection on a sensor.

  • check the IAT connection. I bet this is the root cause as intake air temp can cause rpm hunting. I believe you can display this data in INPA.
  • any other elect connection that had been removed/installed.
 
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