Idle noise ,air leak?

[1843lamp]

My stock 87 Es just developed a lumpy idle ,and the engine has a hissing ,air type noise near the back of the head on the firewall maybe under the intake manifold ,I can not detect any hose or gasket leaks ,what could be the cause?

[MrBurgundy]

Get a smoke test done.

[325e '87]

Look closely at the vacuum line going from the throttle body to the brake booster. The fitting that connects the hose to the metal booster drum makes noise onmy car. Part of my to do list for today

[1843lamp]

Yes ,I will take another look at that area ,the sound has increased to sounding just like a hissing water leak at idle ,the idle is still lumpy but has not actually killed yet .When you step on the accelerator the noise mostly goes away ,very strange situation my other car of 18 years never was like this...I think over the last three weeks the noise is louder .

[e30davie]

Check all of the things made of rubber that are attached with a hose clamp. Each one of them is a potential air leak that will cause what you describe.

the noise goes away when you stomp on the gas because the vacuum goes to zero.

[tomstin]

Vacuum line under the throttle body that goes to the charcoal canister.

[1843lamp]

I have finally had a chance to look at the problem again.It has steadily become worse,it will not idle ,it has stumbling and a little backfire at 65 that is really hard to hear .Also noted ,when I stop the car and get out there is a really bad acrid smell and the exhaust seems to have a little cracking and popping sounds.Yesterday I spray leak checked the engine and this time found no 6 fuel injector appears to have an air leak ,I am wondering if the smell and exhaust symptoms are related?

[1843lamp]

I took the fuel rail out this morning to check for a leaking o ring on the fuel injector all looked good .What I found was a section of manifold gasket right at no 6 injector standing 1/4" straight up from between the intake manifold and head.I removed the intake manifold and found the gaskets to haven broken up and shifted on almost all flanges and the gasket was totally black ,looked terrible ,nothing like the green ones I installed two years ago ,I have never seen anything like this in 40 years and more working on cars ...these were brand new gaskets .