Greetings. We have an '85 300TD with 180k miles. My son has inherited the car from me and is his daily driver. We have replaced many of the key components, and are now Looking at fixing the turbo. The turbo has not functioned "normally" for several years, but we have not messed with it since the car runs great. I personally know how the car used to perform and the sound it made when it was working correctly. There has not been any "whine" or noticeable boost for some time now.

Visual inspection the other day shows that the turbine is spinning even at idle. I don't know if that is normal. I'm just a somewhat-experienced shade tree mechanic, but it would make more sense to me that the turbine would only spin when the turbo was engaged. Is that correct?

I'm wondering if perhaps there is maybe a valve stuck open (waste gate? apologies for lack of the proper knowledge and terminology). Wondering if there are some suggestions on how to test this (vacuum or pressure from the connected lines)?

We have had the car for >15 yrs and it's pretty clean, including the engine, and we have replaced most all vacuum lines under the hood, so there's not much visually that looks corrupt.

Thanks in advance for any suggestions and help!