M44 Long Term Fuel Trim 20-25

[FuelCell250]

I just finished rebuilding my 1997 318i with the M44 and an automatic transmission. I replaced the pistons (MaxSil), rings, bearings, timing components, and seals.

I didn't drive it before rebuilding it, as I bought it needing the rebuild. I have about 500 miles on the motor now, and ever since day one I've been having these issues:

- Fast idle, around 1200 RPMs
- Long-Term Fuel Trim of +20 to +25
- Code: P0505 - Idle Air Control System
- Code: P1509 - Idle Control Valve
- Code: P1550 - Idle Speed Control Valve Closing Solenoid Control Circuit Electrical

Here's what I've tried:

- During the rebuild, I triple-checked for correct timing
- During the rebuild, kept a sharp eye out for cracked vacuum lines
- Replaced a severely cracked intake boot
- Cleaned the ICV (now it doesn't work, no buzzing like before )
- Cleaned the MAF
- Replaced the pre-cat O2 sensor ($175, old one was welded in, used plug and play Bosch part)
- Replaced the MAF with another used MAF ($110)
- Unplugged the crankcase vent and plugged it, thinking bad CCV

I'm not really sure what to try next. Any ideas?