[V8] 1990 Audi v8 Coolant temp sensor

[chris brown]

Hello long time since iv'e chimed in. Iv'e got a 1990 v8 and i bought a coolant temp sensor a couple months ago because my engine is running rich and i was told this could be one of the easy fixes for that.   I dont know where on the engine to find this thing i looked around a little but i figure ot be easier just to ask here.   Is it a pain in the neck. 
Engine runs fine with a cold start and after about a minute and a half as it warms, idle gets rough and starts to hesitate and run rich. 
thanks  guys
 Chris 1990 v8