I have an 01 blazer ls 4x4. 90000 miles on it. The engine is making a VERY loud howling noise from the intake side of the motor on acceleration. It sounds like an enormous amount of air is trying to go through the intake. the engine light just came on but they charge 70 bucks here for a diagnostic here and the truck seems to be constantly in the shop :-( Its very loud. I have had the truck for a year, it happened 2 times before but only for a couple minutes then it went away. it has been making this noise for 4 days now, but it stopped for about 10 minutes of driving yesterday and started again. I read that on fords it is the IAC valve, but no info on chevy 4.3's....the howling isnt a grinding or anything like that, its definitely sounding like huge amounts of air going through the intake. engine seems to run ok other than the loud sound. any help would be great.

 

take it by a chain auto store,they will check codes for free. As for the howling are you 100% sure its coming from inside the intake?

 

Post what you find out, mine does it to but only till i get to higher rpms or it warms up then goes away. I`m also thinking IAC or maybe O2 sensor. I cleaned the mass air flow sensor, didnt help any. Sometimes it starts back up when I`m on the highway and running at lower rpms. Thats why I`m leaning more towards the IAC.

 

Mine would stop howling at about 3-3500 rpm when it first started a few days ago, now it does it from 1000-redline. Apparently this problem happens alot on ford motors and it is the IAC valve. I couldnt find out anything on the chevy motor. Hopefully one of the pro guys on here knows whats up, i have sunk alot of money into this blazer trying to get it running rite and so far no luck lol.

 

The IAC is mounted on the side of the throttle body, You can take them off and clean them. Theres also the TPS on the throttle body. The IAC is the smaller of the 2.

 

What first came to mind for me on this, Fan clutch.

 

I thought this also but when I`m on the highway and it does it the truch will back
fire occasionally making me think air fuel mixture issue

 

also check your gaskets, especially the intake. does it do it all the time? does your engine rev or idle really high? if not and only when you're on the gas, it would seem like you have some kind of sealing surface that's failed, and only when the engine is trying to pull large amounts of air at a time. if you smoke you can have a buddy rev the motor and you blow your smoke into the engine compartment and see if it gets sucked in anywhere.

 

I second the gasket check. On my other blazer i forgot to make sure that the part of the spider injector assembly that sticks up through the intake sealed when i replaced it and it would howl really loud from the air getting sucked in around it. Its the part right behind the throttle body where the fuel lines plug into also.

It will throw a lean code as well, so that would explain your code.

 

Ok, I know this is going to sound stupid but I've been working on cars for years and years and when I had this problem it took a bit of luck to find the problem. Mine had the same thing. I looked for exhaust leaks and intake leaks and never could find it. Then one day while it was running I happend to lay my hand on the distributer. Yes, the distributer. The bearing went bad and it sounded exactly like you describe, air type noise. I could not believe it. Swapped out the dizzy and noise is gone. Open the hood and rev up the motor with your hand on the distributer. See if you "feel" it. The backfire also makes sense as the things get a lot of slop in them. Again, I was sure it was air and could not believe it was a bearing. But it was. I hope this is your problem as its an easy fix.

May not be, but def check this as bizarre as it sounds. Had me stumped for about 3 months.