Dan87951

I'm visting with the parents this weekend and my dads 85S is making a hissing sound which gets louder as revs go higher under the center intake runner. What would be causing this? The hissing sound doesn't start until the car starts to warm a little than it gets louder as the revs climb. It really sound like he has a supercharger under there! lol I'm pretty sure it isn't the vacum lines as it sounds more mechanical. Only thing I can think of is idle stablizer?

Thanks

Mrmerlin

you might try looking under the intake for a loose fitting MAF or a cracked air line, use a piece of hose to zero in on the noise

JHowell37

Does the sound eventually stop? If so, it could be the ISV.

Dan87951

never stops

Landseer

Any way to shoot a little audio video clip?

There's a big boot in there, the butterfly valve seals, the TPS that has seals on that same shaft, the intake gaskets, some injectors in the vicinity, not much else.

How is it running?

Dan87951

Car runs great only problem is the hissing sound you hear now directly under the center intake tube. Very weird never heard anything like it. Makes the car sound like its boosted. Gets louder as revs climb. I figured it might be a common problem but it doesn't sound like it.

Imo000

You have a large air leak. Get a can of starter fluid or propane and start looking for the leak.

Dan87951

Weird thing is this hissing sound doesn't start until the car warms up. I will check around for him. Thanks for all the suggestions.

blown 87

vacuum leak

Maleficio

What's a good product to gently release as vapor around the vacuum lines and ports to observe a leak and causing the engine to try to stall?

Mrmerlin

I would be very careful about spraying anything flammable around the intake.
One bad ignition wire will have a quick ball of flames showing up under your hood.

What did you find out by using a hose placed near any of the intake parts and listening??

WallyP

I second the suggestion to use a four-foot plastic or rubber tube stuck in your best ear to be used as a leak location device.

Maleficio

I'm gonna fab up some closed-ear headphones with a long rubber tube inserted in one muff.

Mrmerlin

sounds like great idea Mal

Maleficio

Thanx, MrMerlin.