If you get your car scanned, it might have codes stored.
One way to check your throttle actuator is to swap it out for a new one, but it's not very cost effective as it's about a $1,000 part. :-(
One sign that your throttle actuator is going out is a failing or intermittent cruise control. The throttle actuator is also called EA/CC/ISC module (electronic accelerator / cruise control / idle speed control). All three functions are combined in one part.
Your problem could just as likely be a vacum leak or a Mass Air Meter.
I would take your car to an independent mechanic that specializes in Mercedes.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".