Posted by David Sherman on Thursday, September 21, 2006 at 12:14PM :
In Reply to: rough idle posted by Pat Hazel on Thursday, September 21, 2006 at 11:39AM :
A rough idle is almost always a vacuum leak. It sounds like you've already pinned it down to the vacuum advance diaphragm. You have to buy the whole new vacuum advance unit, but it's cheap. If you're not sure, take a propane (plumbing) torch, remove the burner tip, put a couple feet of vacuum hose on the end of it, open the valve slightly, and with the engine idling direct the propane from the end of the hose to various places where you might have a vacuum leak such as base of carburetor, all around the intake manifold, around anything hooked up to vacuum (brake booster, spark advance, windshield wipers, PCV valve, etc) If you get near a leak, the propane will be sucked into it, which will speed up and even out the idle. It's very quick and easy to find vacuum leaks this way.