Engine Light Help

[Daniel Isaac <isa@philabs.research.philips.com>]

Hello All,
I am having a problem and would like to here some theories.   About a
week ago I had my oil changed at one of these quick lube places.  A
couple of days later my engine light came on and has been on ever
since.  It is
not blinking.   I have already done the coilpack repair fix and I have
taken off my gas cap and put it back on making sure it is tight.   What
else could it be?   Do I need new spark plugs?   I am really tight on
cash and I want to avoid taking it to dealership if at all possible, but
that yellow light is starting to bother me.

TIA
Dan