I have a 2000 Toyota Camry LE, with 147,000 miles on it. At present, when sitting at idle with the transmission in park, neutral, or reverse, there is no noise, everything sounds normal. When the transmission is moved into any forward gear, there is a hissing sound that's very noticeable. I can't be sure from the sound if it's a sucking air, or blowing air sound, but I think it's a sucking air sound.

So, my specific questions:

  • If this is a leak in vacuum lines going to the transmission, can I test for leaks in the same way you would for air blowing, I.E. soapy water sprayed on every vacuum line? It seems like this would not work as well since there's nothing to cause bubbling.
  • If that doesn't work, how would I find the leaking hose?
  • Does it fit the symptoms listed above for this to be a vacuum line going to the transmission? Does it not make the sound in reverse because there is only one reverse gear (not multiple like forward gears) and so vacuum is not used? Somehow this didn't make sense to me because the vacuum would still be present as it's generated by the engine, so the hose should still leak. Any thoughts on why only in forward gears and not in reverse?

FYI I did a spill and fill about 20,000 miles ago, and I watch the color and level of the ATF every time I put gas in it. The color is still bright red, and there is no burnt smell at all. Sadly it's a 2000 so there is no PID for transmission fluid temperature.

Any thoughts on what this could be are appreciated!

  • 2
    check around the airbox and intake hose(s), any flexible component of the intake system, verify clamps are tight and no splits in any "accordion" section. I had the exact issue on a Saab, it took forever to find, the "only in forward" symptom was due to the way the drivetrain torqued on worn mounts, opening a giant split in the intake hose, which was otherwise hidden. Just a thought.
    – SteveRacer
    Commented Jul 18, 2016 at 19:18
  • @SteveRacer I would never have thought of that, thanks! I'll do a visual inspection, and if that doesn't find it, with wheels chocked and my son on the brakes, put it in gear, stand beside it, and hit with carb cleaner, Thanks for the thought, I will definitely check this!
    – cdunn
    Commented Jul 18, 2016 at 19:47

1 Answer 1


Hard to say exactly what is it, but I would troubleshoot using a stethoscope. Have someone sit in the car, set the emergency brake, hold the brakes, and put it in drive. Might want to block the tires too just to be extra sure. The stethoscope will allow you to find the exact location of the sound. Look around the intake hoses, throttle body, intake manifold, vacuum lines, exhaust manifold and pipes.

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