Start with the easy bits first. The distributor cap, rotor, and ignition wires are all suspect if not replaced within the past 60K miles or 5 years or so (plugs within the past 12K miles) but defects in these should cause a consistent problem. The resistor on the rotor frequently fails. Also the OVP can cause intermittent symptoms like you report (many posts on this). After confirming these parts are good move on to troubleshooting the more expensive/time consuming items. However, the backfiring through the intake manifold is indicative of an ignition timing issue which could be caused by a defective rotor, EZL or CPS among other candidates. Mark