I have a 2005 GT, automatic, all stock, with 130K miles on it. It will intermittently have idle problems where it will idle too low (400 - 500 RPM) but then realize the problem and bring the idle back up to 900 RPM. Then it lets it fall back down after a second or two. It will sometimes repeat this slowing down/speeding up once every few seconds. Unfortunately it is intermittent, occurring maybe 2 - 3 times a month. It seems to happen just after I fill up my gas tank, but also happens at other random times. This problem only occurs at idle, and only when the engine is warm. Engine is smooth at any speed other than idle.
Since this happens more often after refueling, I thought the gas cap was the problem. I replaced it with a new one from Toyota. I also cleaned my MAF sensor, even though it looked brand new. I pulled off my Intake
, and the throttle body looked brand new too -- not even the slightest film of dust or dirt. I didn't proceed with cleaning the IAC valve. Should I? Anything else I should check or try?
Perhaps unrelated, when starting the engine in the morning, or after letting the engine cool down to ambient, the idle seems high. It will initially rev to about 2200 RPM, then back down to 1800 RPM after a few seconds. If I let it sit it will slowly rise or fall maybe 300 RPM every ten seconds, until the temp gauge gets to that first angle. Then it gradually lowers the idle as it warms up. I'm in Southern California, so "cold" is only 50F ... not like I'm in the snow. Is this normal? If I recall correctly, my cold engine would idle at a constant 1300 RPM when the car was new. It just slowly got worse over the years.
My car always passes smog tests, and the check engine light has never come on, if that makes any difference.