1992 Oldsmobile Ciera help

Any applicable mil codes? If a spark issue, Use a digital multimeter on the plug wires, engine running. Don't get the leads caught in the fan or anything. One lead touches the wire, the other goes to ground. It's an inductive reading, you don't penetrate the insulation and don't take the plug wire loose. Say 4 of your cylinders show around.5 volts and the other two show about zero. If the two that show zero are on the same coil, could be the coil or ignition module. May not be a spark issue, how about idle air system? A vacuum leak would be more noticeable at idle than going down the highway.