It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It could be a vacuum leak, an idle speed control problem, leaking EGR valve, poor electrical connections, many things is the check engine light on ? Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
check out the crankshaft timing pulley, the capri is known to shear the key and destroy the keyway. just happend to me. i had the same problem, also gave me low compression and low vacuum. so check to see if it sheared or not.
--1991 capri xr2 5 speed