99 Corolla making rattling noises going over the tiniest of bumps

Maintenance/Repairs
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1

Hey Cartalk, I’m absolutely clueless when it comes to cars. I bought a 99 Carolla with 130k miles from a family friend, Randy, who owns a repair shop. The car was brought in with a blown engine as its previous owner ignored its oil needs. Randy put in an engine with 90k miles and tightened the motor mounts. It made the 14 hour trek from Nashville to my new home in Houston, but now the bottom makes a rattling noise going over any bump. I’m not talking big potholes- even tiny cracks cause it to rattle. Some notes:

  1. The exhaust sounds normal.
  2. The sound is coming from in front of me at ground level beneath the hood. Just took it for a test drive and I heard it from both sides as well as the middle.
  3. I don’t feel it through the steering wheel, pedal, or seat. The only thing indicative of a problem is the noise. If I had the radio on at full blast, I wouldn’t know there was an issue.

The check engine light also came on. I took the car to AutoZone and got two errors- the first, P0505, was an air control valve control circuit (probable causes per AutoZone: open or short circuit condition, poor electrical connection, and/or failed IAC motor) and the second, P0420, was catalyst system efficiency below threshold- bank 1 (causes: air leak in exhaust before rear HO2S (heated oxygen sensor), AF sensor error, fuel system fault, and/or faulty catalytic converter).

I come to you, Cartalk, for wisdom. Any ideas? Insight would be greatly appreciated. Thanks!

2

“I’m absolutely clueless when it comes to cars.”

You don’t really have much choice but to find a good, trustworthy local mechanic and take it it.

Removing & installing an engine involves lots and lots and lots of things - wiring and electrical connectors, routing of said things, parts upon parts, nuts and bolts…Its pretty easy to have a few things not quote buttoned up. But someone who knows some things about cars is going to need to give it all a once over.

The rattle sound is first. Its likely harmless - a bit of loose splash shield or something. Or it could be very very harmful - like a bad or loose ball joint or something.

For the other things the place to start is to just check and clean the connections for the IAC valve & downstream O2 sensor.

3

Another possibility for the rattling is a dried/worn/shrunken bushing. The ones that hold the sway bar to the chassis rattle like you describe.

For the rest of it, you’re simply going to need to take it to a good shop.