The throttle position switch sits on the throttle housing and tells the computer what position your throttle body is in, which is what you affect when you accelerate. Very seldom do these fail. Very often does the throttle body get very disgusting, and somewhat stick the throttle "flapper". The very high idle could be a sticking throttle and/or a sticking idle air motor (which can also get very dirty). I would definitely start there. First, clean the hell out of your throttle body and idle air motor, next make certain your air filter is clean so it doesn't get dirty again almost immediately, then, disconnect the air mass meter, clean the connector, and resecure it, ziptie it to the box, as there tend to be problems with the connector working their way a little loose and allowing corrosion to build up.

From what you have described I do believe you could have a coolant temp sensor being mean. What year 850 did you say you have? If it is a 93-95 you can read the codes without autozone.

With the 02 sensor, if your car is running rich because of a failed coolant temp sensor, yes, it will foul out the 02 sensor. Most people will tell you that even though you have a code for the front 02 sensor, you must also replace the rear 02 sensor, because the car will continue to set a code after doing the front 02 sensor. Nope, you don't have to...there is a modification of a cable connector and two zip ties which secures the new sensor, and changes the resistance so that the check engine light doesn't get angry. I can get you those part numbers tomorrow.

Chris