I had a problem that may be similar. When I would come off the highway from driving 60+ mph for any extended period of time, the car would idle high for a short period of time, maybe 10 to 15 seconds. Took it to another shop, my mechanic was on vacation, and they couldn't figure it out, took several trips yadda, yadda, yadda.
When my mechanic returned from vacation, he discovered in about 10 seconds, that it was simply the mixture was too lean. Hasn't done it in 100K miles.
This board, and my mechanic are simply invaluable! It could have cost me hundreds of dollars.