The throttle actuator, or engine actuator, or throttle body sits on the intake manifold, or on a V8 in the middle of the engine. It's primary function is to regulate the air/fuel mixture. They are made by both Bosch and Siemens VDO. Follow the air flow through the air filter and you will find the throttle actuator. They usually cost about $1000 but they don't fail nearly as often as they get replaced. A good cleaning will often solve the problem. I think you have one of the great cars there, and while the engine bay is tight for a DIYer, you're not likely to find anything before or since that is as durable and long lived.