Bought my first car this week!

[davet753]

A vacuum leak, if bad enough, will certainly make it run rough. It can also have unwanted effects on the climate control operation. For instance, when the thermal blower lockout switch started leaking on mine, I knew about it because whenever I stepped on the accelerator with the A/C on, the air warmed up because of insufficient vacuum to keep the blend door actuator pulled shut.

I have always heard that in addition to causing rough idle, that vacuum leaks will cause a slight reduction in fuel economy.

On your Lincoln, the slight vacuum hiss when the headlight switch is pulled or climate control lever operating is normal, and nothing to be concerned about. On your parking brake, there is a vacuum actuator that pulls in when the car is put in drive. If this is leaking, you will hear a constant hissing whenever the car is in drive. Vacuum to this actuator is through a switch on the bottom of the steering column. To check these, just get under the dash near the bottom of the steering column and have a helper to shift through all the gears. There should ne no constant hissing at any time near the switch assembly. If it's leaking, the "quick and dirty" fix is to remove the two vacuum hoses and plug them with golf tees.