I have a 1990 that does idle rough. after driving for awhile, the Bonniville will start sounding like it wants to die at idle (when i am at a stop light). I can also here it through the exhaust pipe. I have also notice that I have a slight coolant problem. I had to add more coolant in less than a week.My hubby believes it could be some kind of idling moduale (makes sense). I just want some opions. I do have 183,000 actual American miles. Thanks in advance.