Well, my 98 OBW has on a couple of occassions suffered from a very high idle first thing in the morning. Now, this is not just the cold engine higher idle till warm, this is more like 1500 to 2000 rpm. The first couple of times it happened, it went away after a short time (a minute or so, or after a firm press on the gas pedal). I thought at that time that it was just warming up, but this last week, it did this for approx 10 minutes. I had to drive off and get my son to school, and get myself to work. While in gear and driving, things seemed normal. As soon as I pushed the clutch in, the engine went right back up. In fact, on a level surface, the idle was high enough to keep me going 25mph without applying gas. It finally settled down, but it has me worried.

 

Anyone experience this before? Any ideas? Like I said, it is a 98 OBW. Has the 2.5 and 5spd.

MY 00 RS did this, and my 02 wrx does it now.

Is it bad?

 

It goes away after a minute or two, and it only occasionally occurs.

My wild guess would be the throttle positioner sensor or Idle air control valve.

I would first check for anything mechanical interferring with the throttle action.

Next time it does it, check under the hood if possible to see if the throttle is fully closed. If not it might be something as simple as a rubber carpet catching on the gas pedal or throttle linkage needing lubrication, or...

I use a heavy rubber (water catching) carpet during the winter and my feet make it move forward bit by bit. Same thing happened to me once and it was the carpet.

I'd look at the IAC valve. I think your engine may have the valve on the throttle body.....if so, you can remove it pretty easily and clean in there and the valve plunger with some brake cleaner.

My 00 OB does same in cold weather. Hard to drive till idle returns to normal after a minute or so after cold start.