Engine Performance problem
1990 Toyota 4Runner 4 cyl Four Wheel Drive Manual 280k miles
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When the truck is at a stop or coming to a stop in first gear it revs like the gas pedal is being pumped and it is not, the brake and the clutch are being used, i tried letting go of the clutch and when it was in neutral the revs continued, but as i was stopped in first i let the brake out and the clutch was in and it was doing it so im not sure whether it is something to do with the brake or the clutch but it only happens when i am in first, i have taken it to a mechanic and he worked for 5 hours and couldnt figure it out so any ideas would be great

Have the idle air control valve and throttle position sensor/MAF