fixed 40 % says open circuit or short circuit to air flow sensor potentiometer or faulty. Possibly,fast idling speed. Test air flow sensor potentiometer. Test wiring, cis-e control unit.
96 usually points to an open circuit some where. Bear in mind this is my 560 manual.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)