Denny offered some great advice!!!! A scope is really great for a tune up. When all the cars went to plug in analyzers the scopes got really cheap! But if you don't have one IMO it's worth the $$$$ to put in on a scope withe a good operator and do the cylinder balance checks Denny described. Another thing I do (I don't have a scope either) is use an ohm meter to check the plug wires, plugs, and most everything else that has voltage going through it..... It's usually something really minor that separates a tune up from a really great tune up!