"whats the best wat to check for vacuum leaks?"

Hi Sal,

I don't claim this as "best", but I use Propane to test for vacuum leaks. It's less messy—and no more volitile— than carb cleaner or other sprays.

Take the nozzle tip off a propane torch and replace it with some snug fitting rubber hose about 2 feet long. Practice with the valve to get a moderate gas flow (not a roaring blast).

With the engine at a warm idle, open the gas valve and poke the end of the hose around each injector for a couple of seconds. If the seals leak, you should hear an RPM change when the propane gets sucked in and burned**.

Do the same around any other suspected areas, like hidden vacuum hose ends and the intake manifold gasket itself.

On cars with the pulley fan, block the breeze by laying a piece of cardboard from the fan shroud to the engine.

**If you use a DVM to "read" the O2 sensor output voltage (O2 disconnected from ECU), you'll see the voltage rise instantly if any propane gets sucked in.

P.S. On future posts, I'd encourage you to put the car's YEAR (drop-down menu choice) up there with MODEL, as I did here. The year cam make a big difference, and it's no fun searching for clues in a log thread like this one.

P.P.S. Here's an Idle Air Control (IAC) valve from the photo gallery. I used the EDIT tab to come back here and add it. (The EDIT "window" is open for about 2 hours. After that you get a "too late" message.


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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.