You are having your share of troubles.
The manual says "Current to EHA implausible." That is not one that I have seen. It sounds like the ECU is getting a set of inputs and is being asked to send a current level to the EHA that is out-of-bounds of it's program.
The only thing that I can think of is that either the decel micro switch or throttle position sensor are bad and they are sending signals that the ECU recognizes as inconsistent. Not being able to figure it out, it shuts down and sends out a constant 90%.
Wish I could help more, but the manual does not give a remedy for this one.
Maybe the techs have seen this one before and can help.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe