You definitely will get an increase in idle speed if you adjust the mechanical stop. I 'tweaked' on mine a bit and noticed no adverse effects.

Re: the EGR, mine was plugged and I checked all the various passages until finally got to the port where it goes into the intake plenum, just past the throttle body. It's on the floor of the intake passage. I was able to pull back the throttle body enough to get a wire into the passage and clean it out. It was full of gummy deposits. If you can find no other obstructions you may want to check there. If it's blocked badly you'll barely be able to see it.

BTW, lack of EGR can cause pinging in itself. You'll want to get it fixed regardless, as EGR lowers combustion chamber temps and Isuzu exhaust valves sure don't need any more heat!
HTH...........ed