Is this a vacuum leak?

[DarkMesa8]

1995 GT

Underhood while car is running, I hear a hissing which automatically would appear to be a vacuum leak. Its around the IAC valve. So, I used an entire can of throttle body cleaner, and sprayed it on the upper intake gasket, and the lower intake gasket. The engine didn't so much as cough.

So, I sprayed the throttle body gasket, nothing. I sprayed the IAC itself, nothing.

The hissing is very audible. I'm now convinced that its the IAC valve itself, are they supposed to hiss?

I unplugged the AIC, and it didn't change anything. Didn't throw a code (I didn't drive it, though), but it idled the same. I turned the car off, and than back on, and it didn't rev to 1500 like it normally does on startup. Just kind of turned on straight to 1000, and that started to idle. When I plugged the IAC back in, nothing changed, but it started normally.

The AIC is expensive, so I don't want to replace it unless necessary. Is it supposed to be hissing loudly? Is the leak elsewhere?

 

[jrichker]

Use a vacuum gauge to decide if you have a leak first. Vacuum should run 16"-20" at idle with a stock cam, most will run closer to 17"-19". of vacuum.

Use the spray trick to localize the source of the leak only after the vacuum gauge reports a low reading that doesn't increase with a change in engine speed.