94 regal custom hard starting

Ok this problem has been around for a fiew years now, and it's really starting to get the best of me......I just can't figure it out. It starts hard, runs rich, and the fans won't kick on till about 260 degrees, unless you unplug the coolant temp sensor, then they run all the time but pulls a SES light. I have replaced everthing that I can think of.....I really hope you don't want a list of everything I have replaced......everything under the hood has been replaced atleast once. Hope I wasn't to rude about it all, I'm just tired of working on this car, and nothing seems to fix it.

1st - What engine & how many miles?

Does it start hard all the time or just when cold?

It's a 3100, the car has 184,000 miles on it, but the motor has 48 miles on it. It hard starts all the time when it's cold, but sometimes it's also when it's hot, and has been sitting for 15 minutes or so. All 3 motors that have been in the car have done the same thing. Along with both computers, but the second computer did get rid of a slight miss at idle......guess I can be happy that something got fixed with all the new parts :)