[porschefan76]

Troubleshooting code P1126 which seems to be Bank 1 range 1 rich limit exceeded. Initially the car also began idling poorly and backfiring through the intake. Most of this has cleared but P1126 reoccurs after clearing.

TLDR-style roll-up of troubleshooting performed thus far for clarity:

1. MAF - cleaned twice, outputs in Durametric seem good, 15 kg/h and 1.28-1.33 Volts at idle - both increase with engine speed
2. Throttle body, plenum and resonator removed and cleaned - not very dirty and very little oil present, all vacuum hoses inspected and verified connections
3. Fuel filter replaced
4. Fuel pump volume flow tested at fuel filter - 1.25L of fuel collected in 30 seconds (is this a potential problem above specified 850mL??)
5. Fuel pressure tested at fuel rail - 3.8 bar with engine off and fuel pump by-passed, 3.3 bar at idle - meets Porsche spec
6. Spark plugs replaced - old ones were not overly fouled, but electrodes had wear
7. Intake Smoke Test #1 - no leaking smoke observed
8. Crankcase Pressure Manometer - -4.95 to -5.05 inches of water column, re-checked yesterday, no change - AOS appears functional
9. Bank 2 fuel injectors replaced with new Bosch fuel injectors and fuel pressure regulator replaced (while fuel rail was out) - no perceived change or Durametric data changes
10. Bank 1 fuel injectors replaced with new Bosch fuel injectors - engine idles and performs much better, fuel economy returned; Banks 1&2 RKAT (range 1 LTFT) further decreased from -2.15 to -3.5, supporting rich at idle CEL
11. Upstream O2 sensors replaced - Originals still appear functional
12. Exhaust Bank 1 & 2 Back-pressure tested - ~0 psi at idle and 0.5-1.0 psi at 2500 RPM - no obstruction
13. Visual inspection of Cats at upstream O2 sensor port - seem largley intact, a few fractures at outer edges but otherwise intact (further investigations?)
14. Spark plug tubes - small leaks at cylinder 1 and cylinder 5 - will replace soon
15. Power Brake Booster line - Went on deep discount, so purchased - will replace soon
16. Intake Vacuum Test - just learned of Porsche suggested test - At fuel pressure regulator, attach vacuum gauge and look for 5.8 to 8.7 psi of vacuum - will perform soon
17. Intake Smoke Test #2 - will perform soon

Worth noting: Bank 1 camshaft deviation is -8.2 degrees and Bank 2 camshaft deviation is -4.26 degrees. Bank 1 deviation is outside +/- 6 spec by Porsche but not enough to throw a CEL. Don't know if this could be causing the issues?

Still getting P1126 code after 30-50 miles of driving. Thanks for looking, any help is appreciated!