[selway]

My car has a 5 speed manual. When driving for a long time at high speeds (>80 mph, on I10 between SA and El Paso) in hot weather with AC on and then shifting to neutral or pushing the clutch and coasting, the engine idle will yoyo between 100-2500 rpm. The longer I let it idle the worse the problem will become, until the engine finally stalls out. When tapping the gas the engine will run perfectly smooth. There is no hesitation or sputtering. Gas mileage is excellent, and there is plenty of power. I noticed this problem intermittently when driving across the country.

[Omar Marji]

does this problem still occur?

[selway]

The problem has not been solved yet. I can also cause it to yoyo in idle when driving at moderate speeds (50-60 mph) when temps are > 90F, after driving about 100 -200 miles.

[Omar Marji]

well most likely an air leak in your intake

[Johntee540]

How many miles are on the car? What things have you already checked? Any Engine codes? - JT

[selway]

The car now has 100,000 miles on it. I had my mechanic check for vacuum leaks, and he found none. I get an occasional code for "Too lean fuel mixture".