1990 Pontiac Firebird EGR Valve

Everything was running fine, but I did a tune-up. I changed the spark plugs and wire, the distributor ect. After that I started the car and I put it in drive and it started stalling on me. I drove the car home (about 20 miles) when I was driving I noticed that there was a big lose of power and I could hear a hissing like noise through the dash of the car. When I got home I raised the hood and noticed that the EGR Valve was melted. I replaced the EGR Valve and it didn't fix anything, the engine still stalled and I could still hear a hissing noise coming from the EGR valve but this time I could see some smoke coming from the EGR or under it, I couldn't tell. I noticed that I had broke the vacuum line going from the MAP Sensor to the intake manifold, so I fixed it, still no change. The EGR Valve still gets so hot it melts and all of my problems still exist. I have spent hours trying to figure out what is wrong. Do you know?