If you can see the screw, then the pressed in cover had to be drilled out and it's most like been screwed with (hehe.... pun)... See my thread in the FAQ on how to reset it to it's factory position. This isn't going to be the source of your error codes but may further contribute to fueling issues (especially if it's in further than spec).
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.
If you're so inclined I'm always more than happy to accept tips via PayPal. 
Tip Jar ---> 
|