My '88 LeSabre (145K) vin code 3, 3.8L always cranks 3 or 4 revolutions before it starts. When it does start (it always does) it races to maybe-2000 rpm then idles down to a normal idle speed). I bought this car a year ago from a shop that had given up on ever getting it running. After doodling around with it for a while, I discovered It needed a new cam interrupter magnet. After I got it running, I put in a new O2 sensor.
I get no check engine light, and the resistances on the IAC are within spec. I noticed the IAC was not perfectly tight on its gasket, and tightening it up makes the too fast idle come down more quickly now, but it still races when it starts up. I hate this. I just think of how damaging this is to the engine to run fast before the oil pressure is up.
The car also is getting pretty crummy mileage 16.3! Yesterday, I removed the throttle body and cleaned it with a toothbrush and carb cleaner, removed the IAC and cleaned it and the passages from it, but no change in the fast initial idle or cranking or crappy mileage.