When you took the intake tuning valve out, you gave the motor a big hole to breath through, thank goodness the throttle plate was closed and the TPS told the computer to idle so with the open tuning valve hole, the motor started and ran super lean indicated by pops and backfires.
For the "oil in yer intake" plenum, check the intake bolt torque, you may have a coupla loose ones.
Like 'da BlazerLT sez, fix your EGR and check your fuel pressure. Fuel pressure check kits are available at most chain type auto parts stores, get one with the bleeder and you can sample the fuel going to your injectors. If you have a buddy with a '98.5 to '02 Dodge w/Cummins diesel, you can check his lift pump fuel pressure with the same gauge and possibly save him $1200 injector pump replacement. Here's the test port on your Blazer. Turn the keyswitch on to let the fuel pump run a coupla seconds, should be 52psi or better. Does the pressure hold a few minutes after the fuel pump goes off?
