C3 vacuum leak / fast idle

[Dave R.]

Last year I purchased a 1969 Corvette L46 coupe. One of the first things I did was to take it to Contes Corvettes in Vineland, NJ to have them go over the car and give it a tune-up.
When I got it back the guys told me that it was a very nice, unmolested car but, they could not get the idle down where it should be due to a suspected vacuum leak somewhere.
I have been told that I should take it somewhere that has a "smoke machine" so they can locate the leak and make the necessary repairs. BTW; the headlights open normally but, the wiper door has stopped working. This just happened after I installed the retaining clips that hold the trim piece on the wiper door.

Is a smoke machine something that I can simulate at home; I don't know of any shops locally that would have such a machine that I can trust.

[Michael W.]

Re: C3 vacuum leak / fast idle

If you suspect it's the system that controls the lights and wiper door,temporarily disconnect the vacuum line on the intake manifold and plug the fitting.

If your idle quality improves, you've found the culprit. There's plenty of troubleshooting guides available on line to track down the exact location of the leak(s).

It's not rocket science, just time consuming.

[Jack H.]

Re: C3 vacuum leak / fast idle

You don't need a smoke machine to troubleshoot Shark vac leak(s)... Most of the catalog houses offer phamphlets that describe how the system works and that's the first place to start.

One you understand the dual role vac plays in the system--two sides in parallel: one for servo (actuation) and the other for control (where/when to apply vac), you can mentally model what's going on. Then, walking through the system from beginning to end with a vac meter will rather easily uncover where fault conditions exist.

Another 'trick' pro mechanics use is pretty simple. Park the target car in the garage and station a second vehicle (family car/truck) just outside with its engine running at idle. Connect a LONG vac hose to the outside vehicle and run the hose into the garage and shut the door.

With the target car off, connect the long vac hose to the Corvette's vac system in place of the intake manifold vac source and then begin to trouble shoot. In the relative quiet of working on your car without the engine running, you can better hear leak sources as you troubleshoot the system...