1965 Ford Mustang idles rough

With doing a tune up, check the distributor cap to make sure it is on correctly. Then check the firing order going to the spark plugs. Had a 1966 Mercury comet and did a tune up. Took and replaced the wires, took them off all at once my mistake should only do one at a time, unless they are labeled. When I put them back on had two wires crossed. When started did the same thing you have described. Check the firing order to make sure they are on correctly. If you had removed the distributor itself then will have to bring the number 1 piston to tdc and resetl the distributor. First check the plug wires so they are in the right firing order.