Mercedes 380SL

I own a 1982 Mercedes 380SL. Fully restored with a new 8c engine put in about 3 years ago. My question is what can cause the car to die when put into drive? I was stopped at a traffic light when it stalled. I started it and it sounded fine until I put it into drive and it died. I had it towed and the mechanic said it runs fine. What can cause this?

Suspect overvoltage protection (OVP) relay, idle air control (IAC) valve, fuel pressure regulator, and fuel pump relay, along with vacuum leaks.

Thanks for the reply. It happened again yesterday so I will take it back in. I will mention the items you listed. Thanks!!
Jeri