More likely the engine temp sensor is marginal. That's what tells the ECU where to set the IAC and also sets the fuel map for the engine temp. If it fails to sense the engine is warmed up, it continues to pour more fuel to the engine and runs the IAC in warm-up mode. The temp sensor is test-able, but I don't have the figures in front of me. The E30 Bentley has the info you need.
Quotes to live by:
guessing gets expensive
nothing is more expensive than a cheap BMW
Ken Kanne, Silverhill, AL, Honorary Forum Grandpa/Craigslist addict/Hoarder of all sorts of stuff
1995 318is "Bebe"; 1993 325is "Elvira" 1985 635CSi "Katja" 1984 633CSi "Sylvia"
I NEED A NAP, DANG IT!