Engine Rattling/Buzzing/Fluttering

Hi all,

I have a 2010 Prius with 197,000 miles. In the past year, I've heard the engine make a rattling/buzzing noise under acceleration. Nothing like the chunky EGR rattles, this is more like a dieseling/dried-beans-in-a-can noise. Watch the attached video with headphones. The noise is heard between the 0:09 and 0:13 marks.

• The noise is easier to hear at speeds less than 25mph, but I've occasionally heard it at speeds above 70mph.
• The noise is intermittent. Similar conditions of driving and weather do not consistently reproduce the noise.
  • However, the noise happens more often in the Arizona summer than winter.
  • The last couple of "fast" turns from a standstill (eg heavy acceleration while also turning sharply) have produced the noise - oil/fluid starvation?
• Keeping the oil topped off, something I started about 6 weeks ago, helps reduce how often the noise is heard, but it still comes up.
  
• So far, it's only a noise, no vibrations are felt in the cabin or steering wheel
  
• My mechanic says that it's okay for a prius of this age to make the noise as "the cylinders shake and tremble as they move up and down inside the block" which doesn't give great comfort to me. He also said the spark plugs look clean. The spark plugs have 60,000 miles on them.
• I have not checked the EGR circuit

Any ideas what it could be?
Follow-up question, anyone have mechanic recommendations in the Phoenix metro area?

 

bbrages, thank you for the reply. I'll take a look underneath and see if anything is loosey-goosey when I do the oil change and coolant change. Sorry for the late reply, I kinda thought Priuschat would send an email update when someone replied to the thread.

 

Mendel, I've had the Prius for 14 years. Thank you for showing me the preference page.

Currently reading the through both the head gasket and EGR cleaning posts on this forum, and it looks a little daunting. What other clues would there be to pinpoint the issue? I will be underneath the Prius in a couple weeks to change the coolant and oil.

Another stat which may be useful. Driving around Phoenix, AZ in 110°F air with the AC set to 77°F blowing at 3 bars, the Prius shows 40mpg. On the North American East Coast (Georgia) where temps are cooler, driving around town using the same AC settings, the Prius would show 50mpg.

 

Thank you for the tips and video. Ordered a borescope from McMasterCarr today. Will take a look next weekend. Not easy to work in the Arizona heat in the evening

 

Alrighty, here's an update.

1. I inspected the cylinder heads. Black as soot which is a relief, and the images are attached. Some of the images are super exposed as the borescope wouldn't bend easily and caught some of the metal housing that holds the ignition coils.

2. I was going through the maintenance history again while i'm digitizing the records, and I found the EGR valve was replaced and reprogrammed in 2019/05 at 148,000 miles. The dealership here in Phoenix also recommend a premium induction service as there is excessive carbon buildup on the throttle plate. My hunch is the intake manifold might need a good cleaning.

3. I changed the oil and both coolants last weekend. The underbody panel that sits under the oil pan is exceptionally sooty. Before I changed the oil, the dealership says the tech found a timing gasket leak which explains the all the buildup. No idea how long it's been leaking, previous records do not indicate a leak.

Here's another video of the sound that I captured as i was in the last stages of topping off the new engine coolant. It's the chunky sound that pops and clicks seemingly at its own rhythm:

I think the the timing gasket leak is a good clue, as the timing chain could be rattling louder due to oil starvation. Pulling the cover off and fixing the gasket looks pretty intense, so I'll start small with cleaning the intake manifold and throttle body, and inspecting the PCV and stainless-steel EGR pipe and see how that works out.


Side note: i found the spark plugs have 80k miles on them NOT 60k as shown in my original post

 

So I cleaned the intake manifold and EGR circuit over the US Labor Day weekend. It was grueling and stressful since there was so much buildup and I was kinda freaking out I wouldn't have car by this morning. Some before and and after photos are attached. Didn't get a chance to snap photos of the intake manifold or most of the clean pipes, but i did get the EGR cooler completely clean with a pressure washer.

Last night I reassembled everything, and the computer is throwing error codes:

• P0113 (Stored) Intake air temperature circuit high input DTC Severity 2 of 3. Repair immediately if drivability issues are present
  
• P0102 (Stored) Mass or volume air flow circuit low input
  
• P0108 (Stored) Manifold absolute pressure/barometric pressure circuit high input
  
• P3190 (Stored) Poor engine power
  
• P0102 (Pending) Mass of volume air flow circuit low input
  
• P0108 (Pending) Manifold absolute pressure/barometric pressure circuit high input
  
• P0113 (Pending) Intake air temperature circuit high input
  
• P106A (Pending) Evaporative emission system pressure sensor - manifold absolute pressure correlation
  
• P0102 (Permanent) Mass or volume air flow circuit low input
  
• P0108 (Permanent) Manifold absolute pressure/barometric pressure circuit high input
• P0113 (Permanent) Intake air temperature circuit high input
• P3190 (Permanent) Poor Engine Power

Scanner: Innova 3170RS


The PCV valve hose not connected when I first cranked it, so I connected it which might explain some of the errors.

Afterwards, I double-checked every connector and hose, and they are all connected firmly in place. I let the Prius idle for about 5 minutes and it sounded normal. I also drove the Prius with the windows down for 1.1 miles at average speed of 25mph and it sounded normal.

Some other threads talk about a drive cycle that can clean some of these codes. Is that something I should try?
Also I did not clean the sensor that's at 3 o'clock on the throttle body because, well it's a sensor, and those don't mix with liquids or aerosols. Should I just buy a new one?

 

Huh, must have been premature concern, because after my morning and afternoon commutes, the CEL is gone!

Annoyingly, I still hear the buzzing/rattling, but not as frequently.