It occurred to me last night that the SAP air hose hole in the intake that I had plugged with a rag and zip-tied off while I waited for an appropriately sized rubber cap to come in may be screwing the DME up by adding too much intake air to the mix. I had a problem years ago where the intake boot dislodged and the car wouldn't idle and this seems very similar.

The cap had come in so this am I installed it over the fitting in the filter box where the SAP hose attaches, and zip tied it securely. The car started and ran fine all morning while I ran errands. At first it was seeking an idle a bit lower than that commanded by the DME (600 commanded and the motor would hunt around 580 RPM, then up to 600, down to 550, etc. Sounded cool at the tailpipes, but eventually she worked out to a nice 600 RPM idle, I imagine as the DME learned.

So problem solved...except not so fast. Since I'm popping codes for the SAP electric valve and the special vacuum driven valve that opens in the 4.6 air box at higher RPM (My box is the 4.4 box tho) and uses the same electric vacuum control valve that the SAP system does, I grabbed my old electric valve and plugged it back in. Voila, one code (SAP valve) gone and no service engine light, however, once I started the car up, it dropped down to idle and immediately died. I started it again and it found an idle, so I revved it and it died again at idle. It seems like a textbook intake boot leak, but I've checked and rechecked everything and its tight as a drum from the box to the manifold.

Unless this is a bizarre coincidence, I suspect this could be entirely self-induced by my deleting the SAP system. Seems weird that plugging that little valve back in would cause the motor to not be able to idle, but who knows what the DME needs to see as it learns.

More to follow when I take it back out and see if it will adapt or keep dying at idle.

***Update***
The car ran fine over a 20 mile round trip of both highway and city streets. Strange, but I'm happy about it. Perhaps simply plugging the SAP electric valve back in forced the DME to relearn the idle. The valve did make the SES light and SAP code go away. Now I need another software solution.

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Current
Original owner 2002 E53 X5 4.4i to 4.6i swap
2026 G80 M3 6 spd
2025 G06 X5 50e
Former
1972 Audi Fox
1986 Saab 900S
1996 BMW Z3
1998 BMW E36 M3 Sedan
2004 BMW E46 M3
2006 Audi A3 Quatro
1993 Mopar 318 Jeep Grand Cherokee
2015 V6 Jeep Grand Cherokee