My first view of those FI cars was to verify the action and stability of the thermostatic warm-up control. Ilde air speed is controlled by adding air through the idle air screw. There are two other sources of air: the closed throttle plate and the auxlilary air valve. This valve is under the thermostat in the injection pump.

The thermostat pushes the airslide closed as it warms up. It changes mixture at the same time. A properly working device with be fully shut at probaly 140-150 degs. It has to be shut before operating temp as one doesn't want a varying mixture or air source while in operating temp.

To test pull the airfilter off the thermostat (on back of injection pump) and plug the hole with a thumb. When cold this will kill the car. When warm it should not alter the engine speed by more than 50 rpms. One will still feel suction but the change in rpm is the test. One should reach the final state of this valve before operating temp.

Timing also can change the idle speed a lot. Verify that there is minimal centrifugal advance in the idle speed range. If centrifugal advance occurs at 1000rpms the advance with take you a few hundred rpm higher as it advances.

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