99 RX300 Low Idle at Startup

I would check the mass air flow (MAF) sensor in the engine air filter housing to make sure it is clean, and check the Idle Air Control (IAC) valve. Clean the MAF sensor with brake cleaner by squirting a little in the opening that protrudes into the air filter housing, and letting the excess liquid drip out.

Clean the IAC valve in the throttle body housing with carburetor cleaner.

Thanks, Ray, I was hoping I would hear from you. You have an excellent reputation for supplying correct answers!

I cleaned the MAF sensor as you directed, and it had no immediate effect on the problem, However 3-4 days later the problem disappeared completely. I should also note that the weather has cooled off considerably during that time. This what makes me think it is temperature-related. I haven't had time yet to clean the IAC valve, but shouldn't I use a special O2-sensor-safe cleaning fluid? I thought carb cleaner could have detrimental effects on O2 sensors, and since I just bought 2 of them at $200 a piece, I have no desire to do that again soon!

Anyway, since it's working normally now, I plan to let sleeping dogs lie.

Thanks for your quick and accurate reply!

Stephen Clark

******** Hi Stephen,

Thank you for your kind words.

As it turns out, the '97 Avalon that my daughter is driving started to exhibit similar symptoms to what you described. I wanted to see if just cleaning the throttle body would do the trick, and it seems like it worked. It has only been a day, so we'll see if the fix holds up.

It is OK to use throttle body cleaner, although carburetor cleaner shouldn't harm the O2 sensor. Some automakers like Ford use a coating on the inside of the throttle body that could be damaged by carburetor cleaner, so the proper stuff to use for coated throttle bodies is throttle body cleaner. Toyota did not use that coating in '99, and as far as I know, Toyota still does not coat the inside of the throttle body so carburetor cleaner should be safe. If that doesn't work, I'll work on the IAC and MAF sensor. I'm pretty sure that the condition will return so I'll work on the IAC next.

Carburetor cleaner leaves a film when it evaporates so that is why you shouldn't use it on the MAF sensor, which has a fine heated wire. Brake cleaner doesn't leave a film when it evaporates.