I have a 66 fastback with a beefed up 289. It has been running great with no issues all summer. This weekend I was leaving a car show, and the car died. For some reason it sounds like the engine is missing when the RPMs are below 1500, and therefore will not stay running. Above 1500 RPMs, the engine sounds and runs great with no issues. I dont know where to start. Thank you for the help.

 

is electronic ignition or the ol points and condenser?

 

my first thoughts as well..

If points, check the gap/dwell

 

It is all electronic.

 

It could be a million things, let's start with the easiest, maybe water in the tank, did you fill up to go to the show?

 

I had a vacuum line disconnected on mine and it caused it to run very rough at idle, but it ran like a champ at higher RPM's. That may be somewhere to look.

 

Post pics of the plugs first so you don't waste your time chasing things down that aren't there.

 

I just pulled the plugs and they look like new, just a little oil on the seat. When I have the engine running, every once in a while a puff of smoke comes off the valve cover, could a leak in the gasket cause my bad engine idle?

 

from around the gasket of the valve cover? then yes it can be the cause, check to make sure you bolts are torqued, i think the recommendation is 10-16 ft lbs better double check that though.

 

Im not convinced a bad valve cover gasket would cause any engine issues other than an oil leak...I am pretty sure you could removed both valve covers and it would run exactly the same minus a huge oil fire.

I suggest you spray carb cleaner around the base of the carb with the engine running to check for vac leaks. spray it all around the base and if the engine changes rpm thats the source of the vac leak.