1988 Chevy S-10 Looking for the timing marks

Remove vacuum hoses and feel for vacuum sucking. If no vacuum then it is faulty. If there is vacuum but unplugging the hose doesn't effect the engine idle then it is faulty. If it has vacuum and it does effect engine idle when removing it then you know it is good.

Sounds to me though like you are leaking coolant internally into engine, possibly worn cylinder rings, and it is being burnt out exhaust causing high idle and white smoke.