On my 85 V6 that I just got running there is a noticeable air intake "sucking" sound at idle. I have never had a Fiero with this engine, is this a normal sound for it? Everything on it is stock. Thanks
I have that same sucking sound. I thought it was a scraping sound at the clutch when I first got my car. But if you put your ear by the air intake on the drivers side rear quarter panel, you'll hear it really pronounced. Many people put a PVC pipe instead of the stock air box(water separator) in the quarter panel wheel well to make a less restrictive imtake, and they seem to say it pronounces that sound too.
------------------ Louis Duet Baldwin, Long Island, NY ~~~~~~~~~~~~~~~~~~~~~ "Blue" <= '85 Fiero GT Stock V6---Stock everything. Trying to keep it 'mostly' that way. ~~~~~~~~~~~~~~~~~~~~~ "Boo" <= '81 Delorean DMC-12 VIN #5835 Stock PRV engine Robertson Equipped Neiland/Delman Engineered Carbed and loving it! (Peugot 604 manifold) ---"Sorry purists"
Yes that's where it comes from, when I first heard it, it sounded like the sound other cars make when you take off the top of the air cleaner housing. Does this mean our cars are starving for air?
If you disconnect the intake hose from the throttle, you can see the IAC inlet where all the noise is coming from. A quick way to make sure you don't have any (major) vacuum leaks is to put your finger over the IAC inlet and see if it immediately stalls the engine. If not, there's either a major vacuum leak or the throttle is misadjusted. The IAC inlet is noisy. Perhaps cleaning it out would reduce the noise (and help it operate at it's best), although I know mine is clean and it's still loud.
The more the IAC opens, the louder it gets. The resting position of the throttle plate is adjustable - the more fully the throttle closes, the more the IAC will need to open. The adjustment screw for the throttle is sealed at the factory, but it's likely you'd find that it's exposed, meaning somebody has already messed with it before. I don't know if the IAC was loud from factory, or if it's a result of the throttle being in the "wrong" position.
Personally I like to let the IAC/ECM have maximum control of the idle and leave the throttle plate closed about as much as it can be without sticking. This does contribute to the IAC being noisy though. It's possible that opening the throttle slightly may reduce the IAC noise without really hurting anything. But if it's still sealed, it should already be adjusted correctly so I'd leave it alone. Some people worry about not touching that adjustment screw. If you move it, just remember how many turns you turned it so you can easily reverse the change. Technically you could also measure it's position by backprobing the TPS. There's an official GM procedure for setting the throttle position. If you're interested in this you might want to search that up. It didn't work for me and I don't remember the steps, but many people follow it. Again, if the adjustment screw is still sealed then there should be no reason to mess with it.
Another possibility - if the engine is idling rough for any reason, the IAC might be opening an unusually large amount just to keep it running. I've had an issue on my car where the IAC will hiss loudly (hear it from the driver's seat) when the engine is first started. It's caused by a misfire that clears up after it runs a bit.
Knocking the divider wall out of the water separator box is a common mod, and it increases intake noise. I wonder if a previous owner did that to your car. You could probably take a look in there and see.
