Recently my '93 Olds 88 has been misfiring a lot a few minutes after I
drive it around.  Took it to a shop and had the air and fuel filters
replaced, MAF cleaned off, and the fuel injection system cleaned out.
They also recommended replacing the spark plugs and plug wires (which I
decided to do myself).  I've changed the back 3 wires and all the plugs
and noticed it was a little better (though the plugs and wire were long
overdue for a replacement).

1. There's a black piece of plastic that holds back the front plug
wires...does anybody know how to pull this off?  It seems like it
should pop off, however I haven't had any luck.  Check out Figure 1 on
the link provided; it's next to the 4th plug wire (directly to the
right)...

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1
5/c3/3d/0900823d8015c33d.jsp

2. Even after replacing 1/2 the plug wires and all the spark plugs, I
drove it around for a while in the neighborhood and it started
misfiring again just as bad as it was before I took it to a mechanic.
Any other suggestions as to what might be causing it to act up?  So far
all I've brainstormed that either the computer has gone haywire,
throttle position sensor has gone to junk, or maybe those front plug
wires are worse than I thought.

Thanks.