After a week of looking for the loud hissing in my engine I found it to be the Insulator Gasket. Its the gasket between the throttle body and intake manifold.
I was experiencing a low idle while in park or at a complete stop like the engine wanted to stall. It's not throwing any CEL's either. Before i found the gasket leak I had already cleaned the IAC, replaced the alternator and a full tune-up. Plugs, Wires, Dist, Dist cap, PCV, fuel filter and air filter. I ordered the Insulator gasket from dealership and will be available in the morning. I've looked everywhere online for a write-up or at least someone else with the same problem and nothing. My question is. Is this a hard job to do on my own. I'm pretty much a noob but not a dummy. Is there a way to fix the leak without changing the gasket? Any advice from my fellow Honda-Tech guru's? Its a 91 Honda civic 1.5 DX sedan with 223K miles. I will post pics of the gasket

 

Here are the pics.

 

General area of the gasket

 

If you want to remove the brown plastic thing, you need to unbolt the throttle body, its 4 bolts. Then you need to remove the hoses that go from the throttle body to the manifold, once thats done you just pull up and the whole tb comes off. Take alot of pics of where each hose goes.

 

Thanks for the info. Will tackle this job on Wens. I'll post up my results

 

Very interesting. I too am experiencing a low idle and lots of shaking when in neutral. I too cleaned the IACV, checked the vacuum wires, did a full tune up, and even adjusted the idle screw. The idle would be fine for a little while, then it would go to 500 rpms again. I'll check the insulator gasket to see if there is a leak. After you replace, let me know if it helped you.

 

Ok, I replaced the Insulator, Insulator gasket and O - ring. Leak is still there. Ugh! I scraped the surfaces clean and installed everything right. I even went back in after installing and used gasket sealant and still a leak!! Is there a certain torque on the 4 bolts or will hand tight work just fine? What am I doing or missing that would still make it leak? i don't know what to do anymore. Please someone help! It leaks mostly under the throttle cable assembly...

 

Here is the diagram... I replaced the Insulator # 2, Insulator gasket #3 and O-Ring #1. Still leaks around the gaskets and insulator.

 

Well if replacing that didn't help, and the leak is causing low idle, and you already tried adjusting the idle screw, then maybe your throttle body is bad or the manifold. You should consider doing a mpfi upgrade.

 

I have considered but I don't want to put too much money into the car. Just a to work and back kind of car. Looking to build a reliable vehicle.