I have a 1990 mitsubishi montero 4wd 3.0L 6cyl engine.I have just changed head gaskets on it and now it won't stay running,it starts fine every time and runs for a min and if I hold the gas pedal it stays running,but as soon as I let go it dies.so can anybody please tell me what the problem could be.THANKS

Check your water, oil, plugs and compression will reveal something.

Sounds like a vacuum leak someplace...