In the morning, as soon as I start my 99 dodge ram, it hisses very loudly. Not only does it hiss as soon as it starts, it'll hiss whenever I touch the accelerator. It kind of sounds like a turbo spooling in a way (even though I don't have a turbo). Also, after my truck idles for a while, it will bog down to 300/400 RPMs, begin to hiss, and then make a god awful sound as if it's about to die. I have already replaced the IAC valve, and am just stumped at this point. Thanks for yall's help!

 

Sounds like a vacuum or intake leak. How's your gas mileage?

 

Sounds like you had a bad IAC valve then replaced it with one that was bad out of the box.
Did you unhook the battery for a few minutes after replacing the old one then start the truck and let it idle for a few minutes after reconnecting the battery?

 

Yea get a new iac from the dealer. Make sure you clean the iac port really well too. And reset the computer so it can relearn idle

 

Typically I sit at around 11/12 mpg

 

I didn't unhook the battery before or after... I wasn't aware that I had to 😂 I just popped the new one on there

 

Sounds good, I'll do that and will be back with an update! I appreciate it!