As I stated earlier. I have had a failure with a distributor cap on my old 3.8 as well, which would run like absolute crap until it heated up. When I pulled the cap, I noted corosion on the electrodes inside. Replaced the cap, and presto.
I have also had the same thing happen on the same engine with the MAF being filthy. When I say filthy, I mean it. The Q-tip came out black. The MAF is an easy one to tackle, I would think. As I said before, a simple way to test is to start the car, and unplug the MAF. If the idle changes, you are probably not in the right location. If the car runs the same, the MAF needs some attention.
Either one should be very simple to test.
Beware of the distrubtor housing though.... A chunk aluminum which was the boss for one screw busted off when I tried removing the cap. I had to use a zip tie to hold the cap on after that
*edit* I never received a misfire code when my distributor cap was cracked. I did receive a low/high MAF voltage code though with the MAF. This was all on an EEC-V vehicle though.