Squealing noise at idle

Squealing noise at idle

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jazzdude

Original Poster:

850 posts

97 months

Wednesday 11th September
quotequote all
For a while now there is this intermittent squeal that happens at idle. It is most prominent when I am doing a base idle set and the rpm is below 800 and sounds like a whining dog. It's quite loud so you don't need to get up close to the engine to hear it.

When the rpm is raised slightly it goes away and also mostly goes while out on the road.

It's not an alternator whine or a fan belt squeal and sounds like it is coming from the front of the engine so I suspect it could be the water pump. The fan belt tensioner was changed a couple of years ago BTW.

For 80% of the time the sound is not there but occasionally it happens for a few minutes and then goes away.

If it is the water pump then do these spectacularly fail and strand you by the roadside or is it something you can diagnose and replace in time?

Penelope Stopit

4,932 posts

54 months

Wednesday 11th September
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A now and again noise from the water pump will very often worsen before the pump fails, it will show its ugly head more often

ed_crouch

1,162 posts

187 months

Wednesday 11th September
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PAS pump?


ric355

156 posts

94 months

Wednesday 11th September
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Your description sounds like it is air flow resonating in the inlet. I have had this myself and it's like the noise is coming from the front of the engine when in fact it is not. The position of the idle screw can affect this significantly and if I'm right you may find a sweet spot for the screw where it doesn't do it. Several mentions of this in the archives.

When I did my ECU conversion the AFM went and was replaced with a bigger bore pipe and this caused it to howl until I tweaked the screw to find that sweet spot after much scratching of my head. Any change that alters the dynamics of the inlet can cause it.

jazzdude

Original Poster:

850 posts

97 months

Wednesday 11th September
quotequote all
ric355 said:
Your description sounds like it is air flow resonating in the inlet. I have had this myself and it's like the noise is coming from the front of the engine when in fact it is not. The position of the idle screw can affect this significantly and if I'm right you may find a sweet spot for the screw where it doesn't do it. Several mentions of this in the archives.

When I did my ECU conversion the AFM went and was replaced with a bigger bore pipe and this caused it to howl until I tweaked the screw to find that sweet spot after much scratching of my head. Any change that alters the dynamics of the inlet can cause it.
That's interesting.

Would it be dependant on slower than 950 rpm? When I am doing a base idle set, and I get the idle down to 600 rpm, it squeals like that, like someone is playing the violin in the engine bay. If I blip the throttle or take off the clamp to the stepper motor hose, it goes.

By playing with the idle screw, are you talking about a very small amount ie, to not upset the base idle setting and would bunging the screw hole with some putty, or rubber or something make a difference?

Power steering is electric smile

Classic Chim

9,366 posts

94 months

Wednesday 11th September
quotequote all
A quick way to check would be to remove your ancillaries belt and run the engine. If the noise disappears your problem is in that area. You can also turn water pump by hand to check for free play or rough bearings. The tensioner is harder to detect as mine seemed fine when spun by hand.
Didn’t think it made any real noise until I changed it, thats when I realised it had been making a slight whining noise for ages.

Classic Chim

9,366 posts

94 months

Wednesday 11th September
quotequote all
jazzdude said:
That's interesting.

Would it be dependant on slower than 950 rpm? When I am doing a base idle set, and I get the idle down to 600 rpm, it squeals like that, like someone is playing the violin in the engine bay. If I blip the throttle or take off the clamp to the stepper motor hose, it goes.

By playing with the idle screw, are you talking about a very small amount ie, to not upset the base idle setting and would bunging the screw hole with some putty, or rubber or something make a difference?

Power steering is electric smile
They would have come with a bung once set as its not often idle screws should need adjusting

jazzdude

Original Poster:

850 posts

97 months

Wednesday 11th September
quotequote all
I had a whine from the alternator, a squeal from the fan belt and hum from the tensioner in the past. All changed and the noises gone.

This is more like a screeching violin and it is constant, not on-off. But then after increasing the rpm to say 1100, it goes.

Usually, I do not hear it when I am out on the road and am at lights or something, but yesterday as I pulled into the drive I could hear it. So I drove down the road, about 10 minutes away to a garage for an opinion and by the time I got there, the noise had gone again.


jazzdude

Original Poster:

850 posts

97 months

Wednesday 11th September
quotequote all
Classic Chim said:
They would have come with a bung once set as its not often idle screws should need adjusting
The lead one? I took that out when I first adjusted the base idle while I was playing with the timing a couple of years ago.

Classic Chim

9,366 posts

94 months

Wednesday 11th September
quotequote all
jazzdude said:
I had a whine from the alternator, a squeal from the fan belt and hum from the tensioner in the past. All changed and the noises gone.

This is more like a screeching violin and it is constant, not on-off. But then after increasing the rpm to say 1100, it goes.
How many turns outward so anti clockwise from the stop is your idle screw. Very weird ?

I can’t quite remember but think it’s only something like 1-1/2 turns. Screw should feel tight. Could be a leak there or just set to far out somehow.

jazzdude

Original Poster:

850 posts

97 months

Wednesday 11th September
quotequote all
Classic Chim said:
How many turns outward so anti clockwise from the stop is your idle screw. Very weird ?

I can’t quite remember but think it’s only something like 1-1/2 turns. Screw should feel tight. Could be a leak there or just set to far out somehow.
Within the 1 or 2 turns off completely closed if recall correctly.

Classic Chim

9,366 posts

94 months

Wednesday 11th September
quotequote all
jazzdude said:
Within the 1 or 2 turns off completely closed if recall correctly.
Which is where you’d expect it to be.
Hmmm!
Maybe worth putting some kids plydo or the like I’m there for a test. Something easily removable.
Air leaks, just have to start narrowing it down,,, thats if it is an air leak.

ric355

156 posts

94 months

Wednesday 11th September
quotequote all
jazzdude said:
That's interesting.

Would it be dependant on slower than 950 rpm? When I am doing a base idle set, and I get the idle down to 600 rpm, it squeals like that, like someone is playing the violin in the engine bay. If I blip the throttle or take off the clamp to the stepper motor hose, it goes.

By playing with the idle screw, are you talking about a very small amount ie, to not upset the base idle setting and would bunging the screw hole with some putty, or rubber or something make a difference?

Power steering is electric smile
As it's an effect of resonation, the actual rpm it does it at is different from one car to the next due to the small variances between systems (and some just don't do it at all). In my case, it would be fine with a few revs on and usually when cold, but get it hot and then you'd notice it sometimes while sitting at traffic lights. Mine was more extreme because I'd changed the system more significantly.

You can do the removal of accessory belt as mentioned but keep the time short for obvious reasons.

Amount of change on the idle screw is quite small (I think mine was around 1 turn). If you can get it to make the noise, just turn the screw (don't bother with clamping the hose etc) and see if it goes away. The ECU will manage the idle rpm with the stepper. Try screwing it inward first as the ECU can still open the stepper while hot to compensate.

jazzdude

Original Poster:

850 posts

97 months

Thursday 12th September
quotequote all
So to check this for sure, if I was to get myself a stethoscope or a long screwdriver and place it in the area around the base idle screw, I would hear it clearly there or is the sound coming out from somewhere else?

psi310398

4,571 posts

148 months

Thursday 12th September
quotequote all
FWIW, not on a TVR, but in my Alfa Spider, I narrowed exactly such a noise, made in exactly such circumstances, down to the bearing on the aircon pump.

Sardonicus

16,310 posts

166 months

Thursday 12th September
quotequote all
Classic Chim said:
A quick way to check would be to remove your ancillaries belt and run the engine. If the noise disappears your problem is in that area. You can also turn water pump by hand to check for free play or rough bearings. The tensioner is harder to detect as mine seemed fine when spun by hand.
Didn’t think it made any real noise until I changed it, thats when I realised it had been making a slight whining noise for ages.
Unless your prepared to try this above ^ your just pissing in the wind IMO rolleyes

ric355

156 posts

94 months

Thursday 12th September
quotequote all
jazzdude said:
So to check this for sure, if I was to get myself a stethoscope or a long screwdriver and place it in the area around the base idle screw, I would hear it clearly there or is the sound coming out from somewhere else?
No that is unlikely to work because the noise reverberates around the whole intake. As I said, it appeared to come from the front of the engine in my case and I could not pinpoint it with a stethoscope; I even replaced the water pump, despite having removed accessory belts to check first. It was difficult to prove either way because the noise was not always present, so with belt off I was none the wiser.

However, try removing the accessory belt as suggested first. It costs nothing to do. Just be careful with coolant temp.


Sardonicus

16,310 posts

166 months

Thursday 12th September
quotequote all
If indeed the whistling/hissing is from the air bleed screw that noise will be heard at the air cleaner end of the trunking/plumbing IME

Classic Chim

9,366 posts

94 months

Thursday 12th September
quotequote all
I was just thinking about a track day were my car seemed a bit slow, check your intake pipe has not collapsed, usually around the air filter area and where it comes through into engine bay. Mine had collapsed to about 1/3rd it’s size after corrosion had got at the wire enforcement, it had actually snapped and holes in the material, proper had its day, that made a bit of a swishing sound.
I’m sure it’s unrelated but any owner still using the O/E air intake pipe should check for breaches in the material and weakness in the steel tubing along its complete length, shine a torch through it, often surprising how many pin prick holes you’ll find.

jazzdude

Original Poster:

850 posts

97 months

Friday 13th September
quotequote all
Just a bit of additional info.

Turning it off today after a run (where btw it did not make that noise during the drive) as the engine turned off, it made the squeaking noise for a split second just as the engine stopped turning.

I then remembered that often the engine makes that same squeak as the engine stops, and it is that noise that I am referring to that it intermittently makes at idle at low revs.

Perhaps some of you also hear that same squeak when you turn the car off.