After adjusting my balance shaft belt, I drove the car and quickly got check engine light and codes 232 in#2 and 241 in # 6. These codes previously showed up after a serious vacuum line was disconnected. That was fixed and codes were cleared for about 100 miles. I can't see how the balance belt adjustment can affect these OBD codes. 232 is fuel trim and 241 is EGR related.
Any ideas or prior experiences would be greatly appreciated. Its a 1990 740 with 16 valve B234f and runs well.
Thanks in advance

Had a car like this, experienced error codes now and then. Usually after starting in cold damp weather, on "old" spark plugs and dirty distributor cap. Clean out or replace distributor cap once a year or so. Have you ever changed spark plug cables, they age. Pretty hot where they run. Use original cables.

Turned out that car ran best on Volvo original spark plugs. They come preadjusted. Worth the money.

The simplest thing is to erase the error codes and check that they don´t reappear immediately. (see FAQ for procedure, simple procedure).

In my car, the throttle stop switch needed re-adjustment, also. In some manuals it says this can´t be done, but it can. Just a tiny bit of readjustment improved idle a lot.

I also experienced that the thin metal thread in the air mass meter had a deposit on it (incinerated insect?). Cleaned it away, and this improved idle characteristics. Be careful if you do this, start by inspecting the thing and if thread looks OK don´t touch it.

Good luck and enjoy this nice engine (as loong as you regularly change the belts and belt pressure adjusters!)