420SEL surging on deceleration
1987 420SEL surges when decelerating in both 4th and 3rd gear...usually occurs between 2,000 and 1,800 (at 1,800 surges back to 2,000, drops to 1,800, repeats) when drifting downhill with foot off the gas (and cruise control NOT engaged). I searched FORUM postings and found similar but different surging problems - not the same as mine. Idle control valve? Dirty injectors? Sticky linkage? Something else?