I would first test the idle valve control current. It should be above 600ma (don't remember actual value).

If you have no current be sure of power from the OVP. If you have poor current like below 500ma but above 100ma I would look for poor solder connections internal to the idle controller.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician