Error code P1128, endless hole of error codes
 

So recently I had my 2002 986 in the shop for an AOS replacement and I immediately got the P1128 error code. I have previously had issues with P0410 and P1411 before this and had my air filter replaced before that. There have been a few other unrelated (I think) times it has been in the shop for maintenance and it's starting to burn a hole through the wallet. I need the car to not have any error codes In order to pass inspection, and I don't feel like paying the labor fee for letting someone else do it anymore. any idea on where I should go from here?

Let me know if there is any other Info/pictures you might need to diagnose this.

Since it showed up after AOS replacement it could be that you have a vacuum leak in one of the intake lines to the AOS. Those get brittle with age.

P1128 - Fuel air mix so rich the system cannot adjust
-Incorrect MAF signal
-Fuel pressure too high
-Leaking injector
-EVAP cannister purge valve stuck open

P0410 SAI signal implausible
-Wiring harness issues
-SAI pump
-Changeover valve
-Air supply lines

P1411 SAI below limit

P0410/P1411 Error Codes
 

I have having a similar issue with these error codes (2002 Porsche Boxster S, 42,000 miles). The check engine light is on and I had a reputable shop look into it twice. My CEL came on on June 21, 2025 and I schedule a diagnostic appointment...the shop did a smoke test and checked sensors...everything checked out but the light and error codes came back...I brought it back and they checked again (another smoke test)...there were no obvious vacuum leaks from what they could tell. The next step would be to take the intake manifolds off and inspect inside...it is starting to get a little costly and I would like to get to the bottom of it.

The car drives fine and I have not noticed anything.

Mike in Virginia

Final update: after going down many rabbit holes, I decided to just go and take the whole manifold off. Upon doing so, I discovered that a wire had been pinched between the header and the manifold gaskets on the side showing the code. I have no clue how it got there but after replacing the gasket and moving the wire out the way, the error code disappeared. Stupid reason, but hilariously simple to fix.

Thanks for reporting back. Number 4 in this chart mentions "Intake air system leaking" so you choose the right work

https://charm.li/Porsche/2000/Boxster%20%28986%29%20F6-2.7L/Repair%20and%20Diagnosis/A%20L%20L%20%20Diagnostic%20Trouble%20Codes%20%28% 20DTC%20%29/Testing%20and%20Inspection/P%20Code%20Charts/P1128/DME%207.8/Oxygen%20Sensing%20Adaptation%2C%20Idle%20Range%2C %20Bank%201%20-%20Above%20Limit/