Found it! The cap on the rear intake vacuum port was cracked. Replaced it and fixed the problem. Thank You! I have a mildly built small block 360 which idles very rough when put in gear. (idles smooth in park). Only recent changes to the motor was I adjusted / took out some slack on the throttle cable. Starts quickly when hot and have to crank a few seconds when cold which is normal for the engine. Checked all the carb's vacuum plugs, spark plug wires, etc. Has me totally baffled. Would taking a little slack out of the throttle cable cause this?