Pelican Parts Forums - roblem with M5 3,8 (s38) engine, error codes

have a Bmw E30, that i have fitted a bmw m5, 3,8 (s38) engine in. The problem is that when it runs without any throttle at all, it does run up and down, and run unevenly.

The engine is from a E34 M5, probably around 94 - 95

We tried to read out error codes and got a
100: 100: Output Stage, Group 1

When i google it , i found a similiar code, but not the same number, we used a universial tool for reading error codes, perhaps this is the reason?

Anyway this was the info i found:

1218 Output Stage, Group 1 This code is stored if there is a short to B+ or Ground at the Output Amplifier Stage (Bank 1). Generally this code occurs with other defects. Causes may be a faulty Idle Speed Actuator, Injector Valves, Ignition Coil on Plug, Oxygen Sensor Heating Relay, Fuel Evaporation, Control Valve, Malfunction Indicator Lamp (MIL) and/or EKP Relay. Delete the code after examining for other faults. If the code recurs, delete code, then disconnect the DME for a minimum of 5 minutes to initiate a reset. Rerun car. If code recurs and no other defects are found the DME is most likely damaged and must be replaced. If the code does not recur and the engine runs properly, ignore.

If i read this correctly it can be a lot of things that is wrong? So the question is, what should i try first, and last? And any tips on how to get it to work correctly ? If i am to change all theese parts, it could be really expensive.

I also found 1 more error code, does not know what this one means?

26: SUPPLY VOLTAGE BATT. +

I anybody got a soulition or some tips i would be really greatfull.