Truck won't idle
 

I have a problem that has me stumped. I have a 1998 silverado with 181,000 miles. About 6 months ago the truck started running rough on deceleration it would skip and sometimes it would cut completely off and then come back on. I have relplaced the distributor cap and rotor, ignition module, coil, the plugs and wires and the problem still persists. It seems that when I relplaced the coil it ran good for a week and the problem came back, and the same thing happened when I changed the module, as well as when i changed the cap and rotor. Most of my problems happen on deceleration like when i come up to a stop sign. The rpms will begin to fluctuate and sometimes it will just shut off. It aslo happens when I let it idle for long periods of time. If it gets warmed up it will eventually start to idle roughly and then cut off. As I am about to get frustrated with this thing any ideas would be appreciated.

EGR valve maybe? Is computer throwing any codes?

Computer is throwing codes but I haven't had a chance to check it. I checked this morning and I'm not getting any spark. Is there a chance that I got a rebuilt coil and it has already gone bad? Does anybody know the resistance I should get when checking the coil with a multimeter?