[Joey911]

Problem: catless N55 has rough idle problem, which if you have Cobb AP, you will see your fuel trim, AFR and RPM jumping up and down during idle and cruising, because the rear O2 is still working as if there is a cat, trying to trim the fuel to archive 14.7, making sure there is no oxygen left.

Read the whole thing to learn about FT or just the last part: http://www.bmwfan.lt/forumas/downloa...57a1c6d2ad92fd

If it's true, the cause of catless N55 idle problem (even cruising) is simply because there is no cat! And the system is really meant a cat!

My thoughts on solutions:

1. Disable the function of rear O2 completely, so it doesn't try to adjust fueling. If it can be done.

2(??) Add the tiny spacer with a tiny cat another thread is taking about to the REAR O2, it might makes it see "clean air"...??

3. An O2 simulator for the rear O2...??


This rough idle is ugly and I hope it can be fixed!!!

[Dhillon92]

I've had a rough idle even stock, it was just a lot less pronounced. I would only feel a jolt here and there during idle. With catless I also experience a rough idle, I'm in for any results, good ideas!

[Joey911]

Originally Posted by Dhillon92

I've had a rough idle even stock, it was just a lot less pronounced. I would only feel a jolt here and there during idle. With catless I also experience a rough idle, I'm in for any results, good ideas!

Do you have that 3 value fluttering up and down? More like bouncing.

[E90 335xi]

I had this issue while I had the DP, mind you it took a few months for it to surface.

I ended up having stalling issues where the motor would completely die off of idle.

Surprisingly, it was resolved by taking off the BMS air intake and putting the factory airbox back on.

Now that I no longer have the DP, I'm going to try putting the BMS intake on again and see if the results are any different.

[Sidewinderpb]

Originally Posted by E90 335xi

I had this issue while I had the DP, mind you it took a few months for it to surface.

I ended up having stalling issues where the motor would completely die off of idle.

Surprisingly, it was resolved by taking off the BMS air intake and putting the factory airbox back on.

Now that I no longer have the DP, I'm going to try putting the BMS intake on again and see if the results are any different.

Samesies.

I've had 2 intakes become deformed around the collar, causing vacuum leak. Paired with DP, car died at idle all the time - especially on cold starts.

[BKBMW335I]

Originally Posted by Joey911

Problem: catless N55 has rough idle problem, which if you have Cobb AP, you will see your fuel trim, AFR and RPM jumping up and down during idle and cruising, because the rear O2 is still working as if there is a cat, trying to trim the fuel to archive 14.7, making sure there is no oxygen left.

Read the whole thing to learn about FT or just the last part: http://www.bmwfan.lt/forumas/downloa...57a1c6d2ad92fd

If it's true, the cause of catless N55 idle problem (even cruising) is simply because there is no cat! And the system is really meant a cat!

My thoughts on solutions:

1. Disable the function of rear O2 completely, so it doesn't try to adjust fueling. If it can be done.

2(??) Add the tiny spacer with a tiny cat another thread is taking about to the REAR O2, it might makes it see "clean air"...??

3. An O2 simulator for the rear O2...??


This rough idle is ugly and I hope it can be fixed!!!

I've had the same situation but mine only started recently after i took my car in to BMW, when it came out it started doing what yours is doing and I also had a huge backfire that sounded like a shot.

Here is what else I came up with on my Scan Tool:


P0036-H02S BANK 1 SENSOR 2 HEATER CIRCUIT
P0171-SYSTEM TOO LEAN BANK 1

[Joey911]

Originally Posted by BKBMW335I

I've had the same situation but mine only started recently after i took my car in to BMW, when it came out it started doing what yours is doing and I also had a huge backfire that sounded like a shot.

Here is what else I came up with on my Scan Tool:


P0036-H02S BANK 1 SENSOR 2 HEATER CIRCUIT
P0171-SYSTEM TOO LEAN BANK 1

Sounds like a different cause, but the *afterfire* sounds good though haha