Does the AOS when beginning to fail… make a noise that would be intermittent? *NM*

My Boxster is making a screeching sound that does not always occur. The car is at the 80,000 mile mark and my query of the site suggest the AOS can produce that noise. I have opened up the engine bay to help locate the noise but it does not always occur. I drove the car last night with not luck.
What I did notice is a slight hiss when pressing the accelerator that immediately drops off… like the opening of the butterfly on a carburetor, so it may be normal. The sound when it does appear sounds like a belt slipping but is not consistent with revving the engine. I initially suspected a clutch or throw out bearing… but everything performs as normal.

Also… the top of the engine air chambers has a light build up of oily dirt, I plan to use a Kleenex or mist to attempt to determine if there is any vacuum leak.

There is no smoke coming from the exhaust.

I also planned to open the air channel to clean it and check for oil in the air way.

Any ideas?

Thanks in advance.



Edited 1 time(s). Last edit at 03/15/2024 11:55AM by m2. (view changes)

Follow up - the build up on top of the air channels is not oily. It is dry.

My scan there says one of the first, early indicators is a "hunting idle", or fluctuation in your idle - slight increases & decreases in engine RPM @ idle.

JB/SE SoDak
1997 986 - Wolfi
Yankton, SD

"Wisdom is the most perfect knowledge of the most important truths in the right order of emphasis, accompanied by a total, permanent disposition to live accordingly.

-- Br. Francis Maluf, M.I.C.M.

"(School is to be a factory) in which raw products, children, are to be shaped and formed into finished products . . .(m)anufactured like nails, and the specifications for manufacturing will come from government and industry."

-- Elwood P. Cubberley, Dean of School of Education, Stanford University, 1905

"The creatures that want to live a life of their own, we call wild. If wild, then no matter how harmless, we treat them as outlaws, and those of us who are 'specially well brought up shoot them for fun."

-- Clarence Day, This Simian World

Thank you… the idle is stable.

You could have one of your idler rollers of the poly-ribbed belt starting to fail.
That could create an intermittent screeching sound.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

The idler pulley beginning to fail makes sense to me and I keep hoping it will divulge itself to me.
Thank you for your assistance… greatly appreciated.

waiting for it to fail, that's not a good course of action as such a failure could end up being catastrophic. Has your Boxster ever had its belt replaced? Now might be the time to replace the belt & also to replace the idler pulley, IMO.

JB/SE SoDak
1997 986 - Wolfi
Yankton, SD

"Wisdom is the most perfect knowledge of the most important truths in the right order of emphasis, accompanied by a total, permanent disposition to live accordingly.

-- Br. Francis Maluf, M.I.C.M.

"(School is to be a factory) in which raw products, children, are to be shaped and formed into finished products . . .(m)anufactured like nails, and the specifications for manufacturing will come from government and industry."

-- Elwood P. Cubberley, Dean of School of Education, Stanford University, 1905

"The creatures that want to live a life of their own, we call wild. If wild, then no matter how harmless, we treat them as outlaws, and those of us who are 'specially well brought up shoot them for fun."

-- Clarence Day, This Simian World

By divulge it… I mean, actually having the noise reappear while running. I have had the noise occur but have not been able to have it begin again while running with the engine cover off.
I have replaced both the idler pulley and belt myself, a long time ago.

The pulley or something running off the belt was one of my original thoughts… but it doesn’t squeal like a slipping belt.

My next step will be to remove the front engine access to see if the belt is glazed and then remove the belt to spin the idler pulley.

Thank you for your help.

good techniques for diagnosing both belt & pulley issues. What you're looking for on the belt likely shouldn't be glazing because the belt is ribbed & doesn't slip. Look for cracks on the business side of the belt, i.e. the inner ribbed side, indicating the rubber is getting fatigued.

John and Pedro, thank you. I plan to pull the front access cover this week… your directions are of a great help. I’ll remove the belt and look for cracking. It will also allow me to try and spin the pulleys, spin the alternator and water pump.

Thanks again.

This might help:

[www.pelicanparts.com]

And this:

[www.pelicanparts.com]