Harry!!!
This is exactly what has been happening with my car off-and-on for the past eight or nine months.
Campbell's replaced the IAC valve in March, and that seemed to fix things, but only for two or three weeks.
I took it back in a couple of weeks ago, and they did what was called a "hard stop adjustment." That fixed the problem for about a week; it's back again.
(Although when the car is not doing the high RPM thing, I notice the revs drop quite smartly between shifts since having this "hard stop adjustment." Campbells says this adjustment is something the techs figured out on their own; it's not in any of the manuals...FYI)
I drove down to London over the weekend, and believe me, it gave me quite a wild ride returning along the 401 through Toronto....four lanes, bumper-to-bumper at 120-130 kph...and I'm on-and-off the brakes to keep from rear-ending slower drivers.
I'll be going back to Campbell's for a new console soon, and will bring the info the recall on the 98s with me.
This is a major pain...can't shift properly; must be causing premature clutch wear, higher fuel consumption, not to mention the danger involved from longer stopping distances and driving a car that speeds up when you take your foot off the gas.
On a lighter note, I took this complaint to Donnellys in July...the shop foreman there spent about 15 minutes telling me this was "normal."
Let me know how you make out getting yours fixed.
Cheers.
