Volvo: 1997 850, electronic throttle control, vacuum tubes

Question
recently purchased. It rode fine for a few weeks, then encountered sudden uncontrollable acceleration (very high idling and very dangerous). Checked all connections, vacuum tubes etc. Started car up and it drove fine again. Then another incident of sudden acceleration. Now it has a constant very high idle and the engine must be immediately turned off. Malfunction revealed by code was P0410 (secondary air injection system) which apparently is very common in this year and model and does not appear to be the cause of the idling (?).  I took cruise control fuse out and it did not reduce the idle. Research reveals lots of problem with "electronic throttle control". I have yet to find any mention of the acutely dangerous condition of my car by other 850 owners. Thanks

Answer
Charles,
This is the first uncontrolled high idle I have heard of. Is the throttle plate sticking open due to carbon? The hoses to the idle air motor are they broken? Check the linkage rods and cable for binding. Most times their are faults as you have there are codes stored, check again and see if there are any in addition to the SAS.