Why does car run good but while idling rpm fluctuates & engine dies? on 1990 Mercedes-Benz 300TE

Occurs mostly in warm weather and occassionally while running. Thermostat stays pretty much at midrange. Replaced idle control valve and ran good for a while then problem recurred after a month.

Asked by for the 1990 Mercedes-Benz 300TE
I believe this vehicle is equipped with the Bosch CIS fuel injection system (Constant Injection System), and these systems are prone to vacuum leaks, especially around the injectors. Make absolutely sure there are no vacuum leaks anywhere and fix any that you find. Make sure the fuel mixture is adjusted correctly as well.
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ecu requires programming update to adjust idle speed,