300E 89 running rich

My 300E (89) starts hard most of the time and runs poorly when the engine warms up. When the engine is cold, it runs fine. Many components have been replaced. My MB parts dealer/mechanic says to check the "governor". He says that this component adjusts the fuel mix depending on the temperature of the engine. How do I check this "governor"? He says that it's attached to the fuel distributor. Going by the picture given to me, it has (2) leads attached to it. I see no vacuum lines. Any suggestions.

Thank you.