[R-235]

I would just like to start this out as saying I have fixed many of my vehicle's problems by reading through this site. It's excellent.

Recenty my 1995 S-10 Blazer Vin #W has been idling normally when cold, then runs ruff after warm up. It has a popping/sputter sound coming from tail pipe, and a missing every now and then from the motor.
This started after I replaced the intake manifold gasket. I took it into a dealer to have the engine timed, because I could not get it just right.

While I had the intake off I cleaned the EGR valve (Third time it's been cleaned in 2 years).
When I replaced the intake gaskets I did not see any oil in the intake plenum.

After my blazer started acting up i decided to look into the intake plenum.

I saw oil in the plenum and what looked like oil in the intake ports going into the engine.
On reading other threads I had checked the PCV and valve cover for excessive blow by and it did not appear serious. I did however take the valve on the top of the plenum off and tried to start my blazer. I heard a couple of loud pops (POSSIBLE THE CYLINDER FIRING).

I fear I may have a burnt valve, but before i do anything further i would like your input.

I would also like to add that i had my blazer's computer reprogrammed. i thought the guy had deactivated that egr when he reprogrammed the computer. would the egr still work if it was turned off.

I have replaced cap, rotor, wires, coil, plugs. I replaced these prior to taking off the intake manifold the secind time.