fox dies when in gear

friend has a 1990 fox and says it runs fine in neutral but as soon as you put it in gear it dies..put it back in neutral and runs good..??

I'd start with cleaning the throttle body & air flow meter plate.

it sounds like a problem i had... for me the solution was to tighten the clutch cable but be careful because i tightened the original too far and it snapped mid-shift. you might consider testing it by just tightening the one you have and if that is the problem go out and get a new one so that you dont end up stranded