Vibration at idle......

[Scoop]

Hello.

I have a 74 Challenger with a 340 in it. When the car is at idle, it vibrates, hesitates when starting from a stop, vibrates a lot slow speed, and at highway speeds it vibrates at around 60mph. It seems to cycle through.....vibrates, smooth, vibrates. I'm not sure how else to describe it. Could it be a misfire with the spark plugs? A short was repaired a few months ago in the steering column. I was told only 7 volts was getting to the coil. Was running better for a bit, but the vibration is still there. I appreciate the help I get here. Thanks.

 

[aussiemark]

Start the engine and unplug the spark plug leads from the plugs one at a time reconnect them and check for a drop in rpm and more vibration when unplugged and a rise in rpm and smoother running when reconnecting (use pliers with insulated handles to stop you getting zapped). The cylinders that have little or no change when unplugged will need to be checked further remove the plug and check if it is firing, check the resistance of the plug lead, check the compression of the cylinder and compare it to the others.

 

[moparleo]

Just a ew more questions. The more info you give us, the better the info we can give you. Remember that we can't see your car, engine or anything else. Pictures are always a great help. And more detailed info like, Did you just get this car ? Or did you just put this engine in it ? Is the engine stock ? Any recent work done to car ? Did the car ever run smooth for you ? Answers to questions like these really help us to help you.

 

[Coupe]

I assume you mean a rough idle when you say a vibration.
You should check horizontal play in the distributor shaft. If the shaft bearings are bad , I know from experience that will cause rough idle.