Fuel trims and Hydrocarbons at Idle question

Hi everyone, I am new to the forum and could really use some experts. I recently swapped a bmw 98 s52 cyl engine into a 98 318ti and have everything running seemingly flawless, all obd monitors are ready and no codes in the system. I did not swap the fuel pump or the fuel pressure regulator (3bar) rather than the 3.5 the donor engine originally had. This did not seem to be an issue aside from the LTFT resting at 11.7 on bank 1 and 2 ( I assume that this is the computer compensating for the slightly lower fuel pressure overall )

Now to the actual problem, I have taken this to the smog ref here in CA twice now and failed due to high hydrocarbons only at idle. (I will attach a pic of the numbers)

It seems to me that if it were a low fuel pressure issue I would notice problems higher in rpm and under load in general. On the other hand I thought that it could also be caused by the computer opening the injectors longer to compensate for the lower overall pressure and the fuel trims not reacting fast enough when rpm drops to idle and dumping more fuel than needed causing the high HC issue. ( I might be WAY off on this and could use guidance! )

Thus far I have smoke tested the vacuum system, replaced all injectors, new o2's, new coils and plugs, and quite a few other things but no dice. The computer is clean, all monitors are ready with no faults and the car seems to run flawlessly.

I am running out of ideas! Any info or directions to point me in would be greatly appreciated. Let me know if any other info - Thanks all!

Lean mis-fire will cause the high HC readings... the engine is running lean as your LFTF's are almost +12.

More info needed. What are the STFT/LTFT readings at idle as well as the 02 voltages. What do the trims and 02's do when you increase the RPM from idle? not wide open throttle, just raise the RPM to 2500 to 3000.

Fuel pump could be issue. What are the pressure readings at idle, and when RPM is increased.

Vacuum leaks, timing, low cylinder compression and or a bad CAT can cause high HC.

High Hc at idle generally indicates the fuel ratio is pinned lean, this isn't going to be helped by lower fuel pressure. The fuel pressure is critical it is reference to to MAP pressure this means if the fuel pump it is critical at any rpm or throttle state.

What is an average value at idle of the longterm fuel trims ?
Also you need to look at the activity of upstream and down stream O2 this will give you an idea of if the catalyst is active and a check on the upstream sensors.

Thanks for the info guys, I am going to check fuel trims and o2 readings at idle and 2500rpm this evening and will report back with the results.

Hey guys, just wanted to post an update. I got this solved, I ended up replacing the 3bar fuel pressure regulator with a 3.5 and resetting my adaptations. They are still a little positive at 4-5% but much better than my previous 11.7. I took it into get a quick sniffer test and it passed no problem. Thanks for the help!