Over the past couple of weeks, my 1989 389 dakota's engine idle has developed a progressively uneven/advancing in speed,idle. At times it idles at around 950 and then most of the time (after the first few minutes running)it would not idle less than 1600...in the last few days it idles at 2000 rpm's! I love this truck and I am not readily seeing how to deal with this issue when I look at the carburetor. any input is welcomed.