ok i talked to one tech and he said he never heard of the problem... but he said to start by removing the throttle body and clean it.. then remove the cylinder that was vibrating which is your idle control valve and clean that... he also said if you removed the position sensor and scrubbed it you might have damaged that as they are sensitive as hell and not ment to be cleaned...
start there.. should cost you a total of 5 bucks for a throttle gasket.. cheap start and let me know.... i have some of the best volvo techs in va here so we should be able to get your car fixed....