There is a tech service bulletin which may be applicable. Text is as follows:

03/95-2 M104 WITH HFM INJECTION SYSTEM


In case of customer complaints of high idle (approximately >2200 rpm) for a very short period of time (< 1 second) immediately after cold start, an updated EA/Idle control unit is available from our PDCs. The updated control units can be identified by a software production date of "SW 43/94" and higher stamped on the housing in the area of the barcode label. The following control unit part numbers are affected:

Electronic Accelerator Control Units

Part No. 124 545 65 32 - E320
129 545 05 32 - SL320
140 545 49 32 - S320
202 545 01 32 - C280

Idle Control Units

Part No. 124 545 55 32 - E320
129 545 19 32 - SL320
140 545 52 32 - S320
202 545 43 32 - C280