79 924 - High Idle... Help!!!

[MinnesotaPorsche]

My 924 has been running at an idle speed of between 2000-3000 rpm for awhile now. I can't seem to recall if it started doing this when the weather got cold or not. It will start (usually) and idle normally for 15-20 seconds then increase itself to the higher speed. What confuses me is that it will do this when the engine is cold & continue to after the engine has warmed up to operating temp. Same goes for if i start it warm after being off for a short period. I'm suspecting the problem is either a cold-start valve (5th injector) or cold-air bypass...? Any suggestions would be greatly appreciated.

Thanks