So I found some threads similar to my issue but nothing exactly the same. Anyway, my idle on my 1990 420sel was perfect up until I changed my thermostat and flushed my coolant. While changing my coolant and thermostat I disconnected te idle air control valve connector, the coolant temperature sensor and the other sensor directly next to the coolant temperature sensor. Also while flushing the coolant I got water all over the front of the engine. After I was done with my job and everything was reconnected I started it up. When it started it refer to about 1500 as usual then the idle quickly went down to about 650 or so then as the engine warmed up the rpms slowly crept up until about 1400 rpm. For a few days it was an intermittent problem but now it's constant. Everytime I start it the rpms slowly creep up until about 1400 rpm. Sometimes it will vary while the engine is running between 900-1400. Since then I've cleaned the idle air control valve, I've shaken it and it rattles but I'm not sure if rattling means it is still in good shape 100 percent of the time and lastly I've cleaned the connection for the idle air control valve. None of this has made a difference at all. I'm almost positive it's the idle air control valve but I would like to make sure before I just go out and spend money. If anyone has any ideas or other possibilities it could be and ways to test what's wrong please let me know. Thanks you.