CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Moan/groan while decelerating 2005 Corolla LE

My 2005 Corolla LE makes a low moaning/groaning sound when I release the accelerator between 40-50 mph. This does not happen below or above the said speed range. I can hear it only when it is sufficiently quiet like in quiet mornings or on roads with low road noise. What could it be ? Do I need to fix it and how ?

How many miles does it have on it?
Is it a manual or automatic?
Has it been maintained in accordance with the manufacturer’s recommended maintenance schedule?
Are you the original owner; is this car new to you?
How are the tires?
Where does the noise seem to be coming from?
Are there any other symptoms?

There are endless possibilities, including it being normal. A lot of things happen when you release th gas pedal, including reverse-loading the powertrain, transferring weight from the car’s rear to its front suspension, causing a vacuum buildup in the brake booster (in preparation for braking), and causing a vacuum spike in the system through which the engine draws air (the induction system). The noise could be as simple as a turning of a sway bar in a bushing as the weight transfer happens or a loose joint in the plastic tubing that comprises your induction system.

Thank you for your response.

It has 59 K miles on it.
Automatic.
Yes, maintained per schedule.
I am the second owner. Purchased it at 40 K.
Tires have about 10 K on them and are in good condition.
The noise seems to be coming from lower/middle side of engine compartment on the driver’s side.

That area is where the induction system resides. My guess is that it’s a normal “sucking” sound that would be the result of the vacuum spike.

Allow me to explain. As your engine runs, the pistons continually draw in air through the intake system. When you take your foot off the gas, the pistons are still trying to draw the same amout of air in, but the passage is now blicked by the closed throttle plate. That causes a vacuum spike to occur between the cylinders and the throttle plate. It sucks air past the plate, which ios designed to adjust enough from the suction to prevent choking, but in so oding it acts like a vacuum cleaner pulling air past one of those slotted high-suction endpieces.

To be on th esafe side, you can have it looked at, but I’d be surprised if it were anything more. The fact that you can only hear it under optimal sound conditions suggests to me that that’s all it is.

Thank you mountainbike for the detailed explanation. I think I will watch it and see if there is any deterioration in performance like mileage, CEL turning on, the noise getting louder, etc. If so, I will take it to a mechanic.

What still confuses me is the specific speed range within which I hear the noise. I will watch it and see how it goes

Thank you once again for your advice. I really appreciate it.