Definitely, the throttle bodies will buzz or sing when the ignition is on, engine off. Sounds like you are running only on the driver's side which is connected to the throttle cable. Check the fuses in the base module in the coffin box and make sure all are good.My car is def in limp mode. ABS and ASR lights on but no warning triangle. It revs all the way but flooring it while driving is very underwhelming, I'm pretty sure a w126 300sd is faster. Okay maybe not that slow but not v12 benz fast.
After some research I learned that the throttle bodies/ETA's should buzz or hum when the key is in the run position. Mine do not.
From my readings the ETA harness may need to be rebuilt or the EGAS module. Which might be something I'd venture to do myself.
I have a check engine light and hopefully a buddy can bring his SDS over next week to read the codes.
Having neither throttle body buzz is unusual. Usually one side will go bad first.