Engine misfires, 2000 envoy

I have a problem I have been chasing for a long time now. The engine missfires when it is what I would consider cold (meaning the gauge may say it is warm, but put it on the highway and get it completely up to temp.) I have changed the plugs, wires, cap, rotor, and ignition coil. It seems to be really bad when it is wet out or if the vehicle sits for about two days without running. Sometimes it is fine for weeks then it is terrible. It will ocasionally bring up an engine code, it reads (multiple random cylinder misfires) I also changed the fuel pump because the sending unit went out...
Any help is greatly appreciated.

could be a couple of things, shell gas was plugging the popets in the injectors up here in canada. I don't know if you guys had the same problem down there.A good injector flush where they run the truck on gm cleans and fuel mix from a seperate pressrized system. Another thing is sometimes the Mass air flow sensor gets dirty Especially if running a K&N air fiter and this causes the engine to lean out more like a bog than a miss.A good cleaning of the hotwire will solve this. make sure it is not on when you clean it i would recommend to remove it and use an air intake cleaner on it, then let it dry before starting the truck.hope this helps, let me know.Chris.

I had tuned it up, bought the plugs and wires at a local parts house. Spent about 90$ for them, I could not get the problem to go away. So I took it to a mechanic, he said you MUST use GM cap,rotor,and wires. Nobody else makes wires that meet the high GM spec. All it did was burn up the wires I put in it.... So he fixed it up for me and it runs great...








could be a couple of things, shell gas was plugging the popets in the injectors up here in canada. I don't know if you guys had the same problem down there.A good injector flush where they run the truck on gm cleans and fuel mix from a seperate pressrized system. Another thing is sometimes the Mass air flow sensor gets dirty Especially if running a K&N air fiter and this causes the engine to lean out more like a bog than a miss.A good cleaning of the hotwire will solve this. make sure it is not on when you clean it i would recommend to remove it and use an air intake cleaner on it, then let it dry before starting the truck.hope this helps, let me know.Chris.