Mechanics

1995 5.7 CHEVY - HUMMING NOISE NEAR THROTTLE BODY

1996 Chevrolet Silverado • V8 2WD Automatic • 145,000 miles

There is a humming-type noise coming from the throttle body. Almost sounds like a mini-fan. I can't figure out what the noise is. I thought it was an IAC valve because the car idled poorly. I replaced the valve and the car idles perfectly but the humming, fan noise is still there.

On a side note, what is the metal hose that is connected from my air hose (that goes from my air box to my air filter) to the engine/exhaust beneath? I'm trying to learn the names for all these parts but there are too many! Anyways, that is really loose and I think I need to get a new one.

Also, there is a thud everytime I start to accelerate. Somebody has suggested that the exhaust may be missing a hanger? I just want to verify that it's a simple fix and not my transmission or something.
Avatar
Philkenroy
February 20, 2011.




The humming noise may be a vacuum leak. The metal hose might be leaking and vibrating around creating the noise. To check for vacuum leaks after you narrow an area down where it sounds like it is coming from, get a piece of sewing thread or light string. Drag it around the seals, hoses, etc. And it will get pulled towards the leak.
The thud noise could be a the exhaust, it all depends on how solid and loud the, "Thud" is. Other than exhaust, I would suspect motor mounts.
You can check this by opening the hood with the engine running, have a friend watch the engine. Put the parking brake on and hold the standard brake while you put it in drive and blip the throttle, see if the engine moves excessively or if you replicate the, "Thud" to any extent. You can also use this method to see if the exhaust is loose. Just have someone looking under at the exhaust when blipping the throttle.
I hope this helps.

I don't have any friends : ( Just playin. Thanks for the reply. Are vacuum leaks serious? Is it expensive to replace motor mounts or are these something I can just tighten?
AD

Tiny
Philkenroy
Feb 20, 2011.
Vacuum leaks can be serious, it depends on how bad they are. Bad ones usually cause the idle to be erratic or high. If it is not doing that it is not top level serious, but it still leans out the air/fuel mixture and lead to problems later as they only get worse.
Motor mounts usually need replacement as the bolts holding them in place are lock-tited and torqued to the point that I have never heard of any coming loose. The have a rubber isolator that suspends the motor to isolate vibration. After years go by the rubber gets hard and brittle and they fail. Usually the torque side of the motor fails first and the other side fails soon after as it is bearing the entire load of the motor. Then the motor can end up resting on the frame and out of alignment leading to bad problems.
Definitely check into the mounts as they are not hard to diagnose.

Well I looked all over for an answer to my next question. So I figure I'll just ask you. What is the idle speed for a 1995 chevy silv 5.7l. Mine idles at about 900 in park and around 600-650 in drive. Is this about right?

Tiny
Philkenroy
Feb 20, 2011.
That sounds correct. So that humming noise might be that loose metal pipe vibrating against some other metal piece and causing the humming noise.
Have you got under the hood and tried to locate the area where it comes from?

Could be.I'll post pics of the metal hose I'm talking about. Might give you a better description. Thanks for helping out by the way.

Tiny
Philkenroy
Feb 20, 2011.
You're very welcome. I will keep an eye out for them and reply ASAP.

Ugh, been raining all afternoon so I haven't had a chance to really get outside and take pictures for you. I was working on my '04 aveo earlier this morning when it was just sprinkling. Actually I should have researched this a little better before I did it but. What if a little bit of water gets in the timing belt area.I needed to adjust the tensioner on my timing belt because it was slipping off the cams. I put an umbrella over the area I was working but I was worried a little water may have still got around the area. May also be some splashing from below. I have both timing covers off too.

Tiny
Philkenroy
Feb 21, 2011.
The timing belt area is pretty much okay as long as major debris does not get into it. Unlike a timing chain, which is sealed inside the engine, a timing belt is, "outside" the motor like accesssory belts. The cover for the timing belt is not an airtight seal is it?
It is usually just a plastic cover that keeps debris out. Moisture can form from condensation as the motor cools down.
So, I think you are fine and a real trooper for fixing your car in the rain under a tarp.

So.I didn't mention this but when I bought the truck there was engine coolant that was "caked" on two lines coming out of the engine so I took it to a mechanic to have them look at it. Today I discovered that the oil cooler lines that the mechanic "fixed" were still leaking. I called another mechanic and he told me with 95% certainty that there was a crack on a flange in the radiator and that was causing the leak. He said he's seen it a million times in the silverados. He said I need a new radiator and that I wasted my money on the other mechanic. After researching these oil cooler lines I realized that they also are important for the transmission. I looked under my car and saw coolant pretty much all over the underbody and what I thought was the transmission. So I guess my question is. How screwed am I? These lines were probably leaking forever before I bought this truck. The thud I mentioned earlier is more like a low pitched rattle. Like the truck is lurching forward or something.I crawled under the truck and tried wiggling the exhaust to see if the exhaust was loose like the car had suggested when I bought it. No movement. Could this be my transmission? It only happens when I first take off. I'm so confused and ****ed off. II think I have made such a huge mistake buying this truck.

Tiny
Philkenroy
Feb 24, 2011.

AD