My 04 xB automatic does this too and so has many other cars I have driven. I assume its normal.

 

I can rule out the injector plugs or any other mechanical problems, especially O2 sensors. The check engine light would be on and you would have a misfire code or O2 sensor code (out of range , slow response,...etc.) The main idle control is the function of the ISC motor in the throttle body. The ECM recieves input from the crank position sensor and NE from the ignition system and sends a signal to the ISC (idle speed control) motor which varies the opening of an air bleed around the throttle plate to control idle speed. When an ISC motor fails the engine usually will stall. The most common cause of poor idle quality is fuel quality. Much gas today is oxygenated and basicly sucks. It can also be very hygrosopic (attracts moisture like a sponge) and also contain various amounts of diesel and other petroleum products (when they flush pipes or switch products at the refinery they don't throw that stuff away, it goes in the discount unleaded tank!). Try a brand name better quality fueland see if that helps, I dont think an oil will smooth out your idle either.~~~~~~~~~~~scott

 

Mine does the same also, 7k miles and I use synthetic oil. When at a light, sometimes itll somwhat fluctuate, go down, then up, down...u know. Seems as if quite a few people have this problem.....

 

don't know if I'd call it a problem. It seems to be pretty normal. I have 12,000 miles on my car now and it's never caused any issues, just something that I notice from time to time. I'm not worried about it anymore.

 

Toyota has a TSB dated 05-20-04 (EG012-04) that addresses rough or low engine ldle at a stop.

http://www.corollatoys.com/parts/scionTSB/EG012-04.htm

However, it is simply a readjustment of the throttle cable. It's an easy, no-tools check to see if your own car is in spec.

George