power lose and miss firing

i have a 96 xj. started miss firing and had a large drop in power. filled her up with mid grade now only happens when the engine is under load and at idle. thinking that the primary coil is going up new plugs and wires and distributer assembly less then 16000 ago looking for ideas to where to start diag.

I would start with three things: 1.clean the throttle body internally with throttle body spray cleaner, including remove the IAC and spray out that passageway.
2. Check the catalytic converter: does it rattle or sound like the insides are loose if you bang on it? If so, you are getting too much backpressure, cutting performance. 3. O2 sensor: when was it last changed? What is the mileage on the XJ? When the O2 sensor failed on me, I noticed poor mileage, lousy idle, a tendency to almost stall on takeoff (with an automatic tranny), and reduced performance.

Re: power loss and misfiring

I would start with three things: 1.clean the throttle body internally with throttle body spray cleaner, including remove the IAC and spray out that passageway. Probably best not to mess with the TPS at this point.
2. Check the catalytic converter: does it rattle or sound like the insides are loose if you bang on it? If so, you are getting too much backpressure, cutting performance. 3. O2 sensor: when was it last changed? What is the mileage on the XJ? When the O2 sensor failed on me, I noticed poor mileage, lousy idle, a tendency to almost stall on takeoff (with an automatic tranny), and reduced performance.

This probably isn't a primary cause, but it might be an additional factor, when was the last time you replaced your fuel filter? While you're at it, check the air filter.

If you're sure it's not an ignition problem, it's more than likely a fuel/air mixture issue.