Help, Loud whistle sound from Mass Flow Sensor?

Phrog · 09-26-2010, 02:42 PM

My car has developed an unusual sound, a loud whistle noise upon acceleration (2000-4000 rpm) from the mass flow sensor. The car is a 1984 911 3.2 stock engine with a K&N air filter. The noise is loud enough to be heard inside the car when driving and changes in pitch as the car accelerates. I have tested without the filter and it has no impact. I can place my hand over the Mass Flow Sensor inlet and that will change the sound. I have no idea what the cause of the sound is and if you have any suggestions I would be thrilled to hear them.
Thanks,
Kevin

ben parrish · 09-26-2010, 02:57 PM

I think it's normal...you don't hear it with the stock filter box in place. My 86 does it also.

Phrog · 09-26-2010, 03:12 PM

Ben:
Thank you but the noise just recently started and I've had the K&N for 10 years. This is a sound I have not heard from any other Carrera and that is why I find it so puzzling.
Kevin

silverc4s · silverc4s's Garage

If you have a stock 1984 3.2, you do not have a Mass Air Flow System. You have a "Barn door" air volume sensor. As it wears, you may notice any number of strange developments...

Phrog · 09-27-2010, 04:36 PM

Bump

kidrock · 09-27-2010, 06:25 PM

Quote:

Originally Posted by silverc4s

If you have a stock 1984 3.2, you do not have a Mass Air Flow System. You have a "Barn door" air volume sensor. As it wears, you may notice any number of strange developments...

I've heard too many bad stories about the K&N setups for our AFM's...maybe too much crud bypassed the K&N and affected your AFM.

Have you noticed a loss of power or any other negative effect that accompanies the whistling noise? Are you absolutely sure the noise is coming from the AFM, and not one of your injectors?

Do you still have the stock 3.2 airbox? If so, I'd put the stock box on to see if there's any change. There are threads on things you can do to bring the AFM back into shape, but they kinda seem like "The Black Arts" to me.

spence88mph · 09-27-2010, 08:13 PM

Mine also makes a loud whistling noise these days

Check the elbow after the AFM, it could be split somewhere, they can crack, also the pipe coming off it to the Idle valve, make sure all those pipes are tight and in good order. Failing that, remove it and check the operation of the barn door, I would imagine if it got stuck somehow during it's motion it might abscure the flow and create a whistle.

turn6 · 09-28-2010, 11:42 AM

Might want to check on the idle speed screw's o'ring...it dries out. If you U can hear it at idle just pushing on it will diagnose.

kidrock · 09-28-2010, 06:13 PM

Quote:

Originally Posted by spence88mph

Mine also makes a loud whistling noise these days

Check the elbow after the AFM, it could be split somewhere, they can crack, also the pipe coming off it to the Idle valve, make sure all those pipes are tight and in good order. Failing that, remove it and check the operation of the barn door, I would imagine if it got stuck somehow during it's motion it might abscure the flow and create a whistle.

Good one, I'd thought about that rubber boot having a crack as well. Also, turn6 recommended checking the o-ring on the idle adjustment screw. Another Pelican had a bad o-ring on the AFM adjustment screw which caused a noise, might be worth a check.