2007 Toyota Corolla LE - engine vibrates when idle, once it stopped at the red light, idle RPM seems low. No issues when I step on the gas

Maintenance/Repairs
#1

Something odd is happening with idle RPM. It seems hesitant. Sometimes the engine vibrates quite a lot. Once it stopped at the red light. Idle RPM seems to vary, sometimes I’ve seen it as low as 400 RPM (if I can trust the gauge), but usually seems at or just below 600.

Strangely, vibrations disappear when it’s at 400 RPM. It vibrates mostly when it’s close to 600 RPM.

No issues whatsoever when I step on the gas and the car starts moving.

What can I do?

Probably unrelated, but I thought it’s worth mentioning: there was a lot of corrosion on the battery cables due to acid leaking, and I had to re-crimp the negative cable recently. The battery issues appear to be fixed for now. I don’t think I knocked something out of whack while fixing the battery, but the idle vibrations started soon after that. Maybe it’s just a coincidence.

#2

A good, properly done throttle body cleaning is a great place to start.

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#3

Is your check engine light on? If it is go to a parts store to get the codes read, post them here, they will look like P1234.

At this age the spark plugs may need to be changed. Very easy to do on this engine, but Toyotas are fussy about plugs. Do not use an equivalent, if your parts store does not have the exact plug, get them from the dealer.

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#4

Yes, get the OEM Denso plug

#5

The Idle Air Control valve may be dirty or defective.

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The IAC valve controls the engine idle speed anytime the accelerator is released.

When these become dirty/defective, not enough air is allowed into the engine at idle, and the engine idles rough or may even stall.

Tester

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#6

How long has this been happening? Corollas of a certain vintage had a rough idle because the idle speed was set lower than it should have been in order to improve mpg in stop-and-go driving. My 2009 idles at 700 rpm or so in Drive after it warms up, which seems about right. If it’s a new problem then listen to the others, especially tcmichnorth and tester.

#7

The mechanic told me Corollas made in the late '00s have this issue if the battery dies. Apparently certain settings are not stored properly on the computer and it forgets the correct idle if the battery dies or is disconnected for a while.

The story checks out because the issue started immediately after I replaced the battery cable (it spent a few days disconnected from the battery).

Now everything is fine.

Also had the battery replaced because it was leaking acid and it was 5 years old anyway.

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