Check Engine Light and car dying in idle

I have a '94 Ford Escort LX. We bought it used. We've continually had problems over the last 1 1/2 years with the check engine light almost always being on and the car dies in idle. The car actually died on an off ramp of I-65 to Indy. We took it in to a mechanic and he told us that it was the PCV Valve and they fixed it, yet, the problems have persisted and gotten worse. It now dies going 20 feet sometimes. We recently changed the air filter and changed gasket cover. I need some big help here, please.