Alright, I would like to adjust the timing on my Suburban and adjust my idle as it is low, but there is this metal cap over the idle adjust screw. I have tried to take it off a few different ways but seriously don't want to break something, is there any thing I could do to get this off easier?

It is a 1991 GMC Suburban with a 350 V8 that has a stage 2 high performance hydraulic flat tappet cam, rebuilt.