Mazda Repair: 2002 mazda protege 2.0LX, honey comb, mazda protege

Question
Hi hope you can help....Wife's Car has been in twice for same issue & now it just happened again. Will drive perfect for a few days then will lose power on highway.This can happen for up to 20 kms. But its getting something as you can go up to 80km/hr but not 100km but then it fixes itself & the issue may not happen for couple days. 1st time code read mis fire cyclinder 3..We changed Plugs/wires/boots & coils on top? Mechanic drove didn't happen, I drove it 50km home didn't happen then happened 2 days later as wife drove. Mechanic said when intermittent hard to chase down but that he did notice that the honey comb in cat. convertor was loose & if it got turned around/plugged the pressure & heat could back up causing code of misfire in cylinder etc. Took car back had honey comb cleaned reinstalled as well as changed O2 sensor (Must be 2 on this car as the one he showed me looked rusty & we changed in summer when we had engine chugging issue)..Again Mech. kept extra day & drove it 160km & it did not happen. I also drove car home 50 km with no issue, drove car into church Sunday 35km 1 way no issue & Monday when wife drove car it happened again.When it does happen the engine light flashes. you can press gas but it doesn't translate to more speed. She describes like its like someone shifts down to 2nd from drive but after that it doesn't run rough just no power to get up to highway speed-80km max. Called Mech. back who suggested I drive for couple days so I can also get a feel for what is happening so I am not giving explanation 2nd hand. He is also doing research. Problem is when I take the car its running fine so its hard to chase down the intermittent issue. its becoming depressing can you help...have you experienced something like this? sorry for the long email....Blake.

Answer
Is the MIL (malfunction indicator lamp) on?  Have you have the code read and cleared?  The ECU monitors the vital sensors.  Of them the main causes of this type fault would be ignition related.  A full set of plugs and wires should have been installed, be sure.  Also the hard plastic boot that mounts to the coil base is known to crack, a small hairline crack here can bleed energy to the cylinder head and will cause that cylinder to dead short, sometimes constant sometime intermittent.  Cross check this area before digging into big ticket items.

BTW - not my specialty area so only general advice available.