My Corolla 2014 has this issue where revs fluctuate quite a bit at idle, sometimes dropping to 4-500 revolutions and going back up. I changed the MAF sensor, cleaned the throttle body, replaced the air filter, replaced spark plugs, and it still does it. Also, there’s no CEL or codes. I took it to my mechanic and they couldn’t find anything wrong with it.
What could it be?
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We call that a parts cannon. I had an 07 Honda Civic that I chased a fluctuating idle on and what finally fixed it was replacing the valve stem seals, essentially caused a vacuum leak. Not an easy job.
How many miles? Regular maintenance?
It’s got 98.5k miles. Car has been serviced regularly.
I found this answer on stack exchange for an 09 - “Resolved (so far :) - last week replaced the timing chain tensioner (Toyota OEM #1354037030). The noise at low load is now gone and the RPM needle remains steady at idle.”
https://mechanics.stackexchange.com/questions/67722/corolla-idle-fluctuation-and-noise
That seems like a plausible solution. I’ll definitely look into it. Appreciate it!
Check your oil fill cap gasket. Just replaced mine after having weird RPM drops when lifting off the gas and now it’s 99% gone. I had replaced MAF and did the idle relearn procedure but oddly this is what helped. You probably have a vacuum issue.
2010 Rolla 1.8, 150k mi
Car Car Nut on YouTube is invaluable