Need Help with Codes on W140

[kustom81]

I have a 93' 500SEL with 140K miles. After leaving the highway last week, the car only had half power. It crawls from a stop and later gets up to speed and runs smoothly. I have no ASR or CEL light on. ( I have been through all that on another S500 I had) I noticed a new tranny fluid leak, so I took it in to get that fixed and have codes read. The tranny protection switch was leaking along with a cooler hose. The codes read were:

17-Crank Position Switch
48-Reference potentiometer
64-Cruise switch
80-Brake light switch

The mechanic thought the tranny went into limp home with the protection switch being bad. He cleared all codes, but 17 will not clear. On start up it runs the same, BAD! Very low RPMS at idle, but no misfire that I can hear. It feels like limp home, but it happens at start up with no ASR light. I know what all those codes mean, except the 48-Reference Pot. I know cruise switch and brake light switch are associated with ASR, but I have no light. Crank position is usually assoc. with hard starting, and I don't have that. What is the 48? The mech. suggests a tune up since I don't know when it was done last. I will do that myself this week end. Mech. said it sounded like it was running on half its cylinders, but I couldn't hear that. He is a very good German car indy. Any suggestions?

Thanks