The end play of the throttle shaft should have a side-to-side movement of ~.03 in, and any excess play should be taken up with thin flat washers. It sounds like the washers and/or the location of the throttle plate is not right. As mentioned below, loosten the throttle plate screws slightly, but before tightneing, run the throttle shaft side-to-side to center the plate and shaft in the throat of the carb. This should give the same shaft width extending beyond the carb body on both sides to where the nut stops when fully tightened. If the washer thickenss is correct, the nut should be fully tightened without any binding at all. Before you reassemble the nut/shaft, put a gob of high viscosity Silicone stop-cock grease into the bushing holes. This will give it a nice leak free seal.
You may have just run into the throttle plate loostening up and needs re-centering.
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon