460 idle problem

Greetings. I have a 1987 f250 with a carbureted 460 motor. 2 days ago the thing would not start. After some generous pumping of the gas pedal it finally fired but would not stay running unless I kept the accelerator pedal pushed down about 1/4 of the way. If I let off the pedal it would bog down and die. After checking a few things, I made a small adjustment to the timing and it will now stay running, but the idle is not steady. It varies from 650 rpm to 1100 rpm about every 15 seconds. It is not driveable as it still wants to die when put in gear. Any suggestions on what to check? Thanks.

Check all your vacuum hoses, especially around the carb, distributer and the one that goes to the transmission(tee's off of the back of the motor, behind the carb)