I have see this happen when the throttle body needs to be serviced here is a guide that will help us fix the problem.

https://www.2carpros.com/articles/throttle-actuator-service

Please run down this guide and report back.

Bought a used vw tdi which instrument cluster was replaced with a no diesel cluster. There is no glow plug indicator light. Any suggestions on how to know when the glow plugs are warm and ready?

The glow duration is controlled by the engine coolant temp, colder the engine the longer the glow, what type of climate do you live in?

I live in the mountains in Arizona. The lowest the temp gets is in the teens. It may have hit 0 a few times.

If you have to hold the key to control glow duration it will be a matter of trial and error extreme cold will require 4-5 sec at least, but yours should be controlled by the ecu so allow about the same time, the glow will shut down peak voltage and continue with after glow voltage for a while so allow about the same time, but you may have to experiment a little.

Thanks, I cleaned my throttle body

just remember it is better to double glow at short duration then over glow and damage a glow plug, good luck with the cold weather.