Car Doctor Q&A: Vacuum Leaks Cause Multiple Issues

Posted by

This week, AAA Car Doctor John Paul gets a question from the recipient of a low-mileage Ford Crown Victoria with a rough idle and a parking brake that won’t release. Can both problems be related?

Q. I inherited my granddad’s 1989 LTD Crown Victoria and it is like new inside and out and only has 54,000 miles on it. As nice as it is it has two problems, from time to time it will stall and most times it idles a bit rough.

One local shop looked at the car and suggested a fuel system cleaning and a complete tune up. After hundreds of dollars spent the car does run a bit better but the stalling and rough running are still there. The second issue is the emergency brake doesn’t automatically release after I use it. When I push on the parking brake it is supposed to release when I put the car in gear but I have to use the manual release under the dash.

Except for these few things the car is great. I’m hoping for an easy fix-can you help me?

Find a Used Ford Crown Victoria at

A. Strangely enough I believe both problems are related. The automatic parking brake release on cars like the Ford Crown Victoria, Mercury Grand Marquis and Lincoln Town Car is vacuum operated. When you move the gearshift out of the “Park” position, vacuum from the engine is routed through vacuum lines and several actuators to automatically release the parking brake.

Any vacuum leak can cause rough running and stalling. Start with a close look at the vacuum release for the parking brake. There’s a vacuum canister on the parking brake itself, and there’s a vacuum switch at the base of the steering column. Sometimes you can hear vacuum hissing from the switch, the canister or the vacuum lines.

You can try pinpointing the problem by pinching off vacuum lines one at a time, starting at the intake manifold until the idle smooths out. Once the idle become smoother, trace the vacuum line and replace as necessary. In addition to the parking brake release many of this vintage Ford products have a vacuum reservoir tank that fail over time and cause poor engine operation.

If the car needs a new vacuum tank, they are inexpensive and readily available online. Replace any vacuum lines that are brittle, to prevent future problems.