Checked codes, nothing at all... Could the TPS be going out but not setting a code or CEL?

On one occasion we had a 98 E320 that had no throttle at all, no codes, turned out to be the pedal position switch (which is a potentiometer up near the brake booster that the throttle cable attaches to). This simply sends a pedal position to the ME that it processes to generate a throttle opening at your electronic throttle actuator (ETA). ETA problems generally generate a CEL, an ASR light, and a lopy idle and no way to get engine RPMs over about 1100 rpm.

I wouldn't guess around at this, take it to a good shop with SDS so they can dig deeper as you are dealing with expensive parts to start parts swapping without the ability to look at live data.