Ive got a 1984 Ford 460 c.i. engine in my motorhome, (37k miles) took it to get smogged and it failed in one of the 2 catagories. Ive noticed a very slight miss while it idles, but the miss goes away (or seems too) as the rpms go up. (about 1700-2000 rpm's)
The smog tech guy told me my problem was at idle as well, so i took it home, installed new plugs/dist. cap and rotor, took it back for a re-test and it actually got a worse reading!
Does this sound like i could have a burnt valve?

 

A burnt valve shows up at idle and as speed increases, the valve will actually seal better. The velosity of air in and exhaust out actually walls off the combustion process. So going down the freeway without a lot of load on the engine you may not feel anything.

Has anyone done a compression test. Or there is a test you can do if you are careful. Find out if your ignition system is not damaged by disconnecting individual spark plug wires, then try them, one at a time. If you engine does not change speed when a plug is disconnected, then you have located the problem, maybe not what it is but certainly where it is. Be careful, those wires can knock you on your ***, maybe even kill you.

 

Thanks for the info Larry....update as of 7/20/04, turned out to be a vacuum leak, apparently the gasket that is between the intake manifold and holley carb is bad. Phew! now that i can handle!
p.s. electricity is not my friend, so glad i didn't have to mess with pulling the plug wires, ive been zapped afew times in my life