I have a 2005 Monte Carlo with the 3.8l non-supercharged engine. When I first purchased the car, I figured out it had a coolant leak pretty quickly and ended up replacing the lower intake manifold with nice Felpro gaskets. Because I wanted to do a thorough job, I ended up getting the upper intake plenum with gaskets as well from Dorman. Initially, when I started the car up and drove it, this sucking noise from the intake was much greater and when I opened the oil cap, the engine would stall. Apparently I forgot to transfer over the PCV valve when I replaced the upper intake so, I got a new one and it quieted way down. I've been driving it around as is for a while and am still getting a sucking noise (louder than normal) and my idle fluctuates after initially coming down from 1500rpm when first fired up. It is also worth noting that when I shut the car off, there is a big release of air noise coming from the engine bay. Any help would be greatly appreciated! Just trying to get the car in tip top shape to save fuel with these terrible gas prices.

 

Do you have a cold air intake or a cone filter in place of the stock intake pieces?

Check your IAC valve on the throttle body also. I had the same symptoms that were caused by a bad IAC.

 

I’ve replaced the IAC valve but maybe it was the wrong one? I know there is certain measurement that they are supposed to be that I didn’t check. Also, when I replaced it, one of the screws broke off so it only has one in it. I’ve tested the car with a smoke machine and spraying carb cleaner around various parts of the intake system and found no leaks. I’ll definitely double check that IAC, thanks

And no, I have the stock intake on it