strange idle problem

[ForOffRoadDriving]

i have a 1990 2.3l ranger that developes and irratic idle when i depress the clutch and let off the gas to make a turn or when slowing down for a stoplight. it toggles between 1000 and 1500rpm and only does it when the vehicle is moving, when i come to a stop it smooths out and you would never know anything was wrong. does anyone have any idea what might be causing this? there is no check engine light on and otherwie it runs fine (burns a little oil, but with 235,000 miles it likes to be lubricated).

 

[ForOffRoadDriving]

i got it figured out, i had my friend from work hook up his scanner but before we even finished hooking it up i noticed that the vaccum line that comes off the intake and goes to the heater controls had a hole in it right where it comes out of the vaccum tree. runs like a top again so im happy.