RS60

Edited...

fast951

Many items can cause rich AFRs.

If it's overly rich under boost, then a possible cause is a pressure leak.

If rich under all conditions (Idle, PT, WOT, cold, hot..), then it's a bit more involved. Start with the basics (not in any order) :
- Clean the MAF with MAF cleaner spray.
- inspect the wiring between MAF and DME.
- if your MAF harness uses a chassis/engine ground connection, then disconnect it from chassis and connect it to battery negative terminal. Note any change in AFRs.
- inspect TPS. Verify Idle and WOT are triggering. You can do this with ignition ON.
- inspect injectors wiring harness, repair if needed.
- inspect engine temp sensor harness, repair if needed.
- set FQS to position #0.
- unplug O2 sensor, note how it affects Idle AFRs.
- if you have a Piggyback, replace it with shorting plug. Note any difference in AFRs. Examine map in PB.

The Motronic Monitor makes diagnostics much easier, use it to examine all the variables as seen by the DME..

Good luck and report back.