Ford Escort idle problem

1994 Ford Escort, wagon, 100k plus miles, 1.9L, manual: Previously over the last couple of years engine stalls and dies when stopped at a red light (mostly when outside air temperature is around 60-70 degrees). This doesn't begin until after the car has warmed to operating temperature and it isn't a consistant occurance. All of a sudden (most recent tank of gas) gas mileage has dropped from 30+ mpg to 20 mpg. Furthermore, today the idle went haywire. After driving from a cold start for about 5 minutes and the clutch was engaged or tranny was shifted out of gear the idle raced to an extreme level and didn't come down. I had to ride the clutch a bunch at stops to keep the engine from redlining. This trip to work was about 15 minutes and was in late afternoon with cool temperatures. But, my return home tonight was without mishap. The idle was normal. Something is obviously on the brink of destruction. Any ideas?