99 RX300 Low Idle at Startup

[Steve]

My wife's 99 RX300 sometimes idles very low when started with engine
warm. A blip of the throttle generally returns it to the correct idle
speed. Seems to happen only when engine is warm. My wife reported that
she often has to start multiple times to get it to idle without dying.
The car has 82K miles, and is current on all scheduled services. Two
oxygen sensors were replaced a couple months ago, but did not affect
this problem at all.

I'm thinking ISV needs cleaning, or possibly a temperature sensor is
faulty. any opinions? Thanks in advance for your suggestions!

[Ray O]

Post by Steve
My wife's 99 RX300 sometimes idles very low when started with engine
warm. A blip of the throttle generally returns it to the correct idle
speed. Seems to happen only when engine is warm. My wife reported that
she often has to start multiple times to get it to idle without dying.
The car has 82K miles, and is current on all scheduled services. Two
oxygen sensors were replaced a couple months ago, but did not affect
this problem at all.
I'm thinking ISV needs cleaning, or possibly a temperature sensor is
faulty. any opinions? Thanks in advance for your suggestions!

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.

[Steve]

Post by Ray O

Post by Steve
My wife's 99 RX300 sometimes idles very low when started with engine
warm. A blip of the throttle generally returns it to the correct idle
speed. Seems to happen only when engine is warm. My wife reported that
she often has to start multiple times to get it to idle without dying.
The car has 82K miles, and is current on all scheduled services. Two
oxygen sensors were replaced a couple months ago, but did not affect
this problem at all.
I'm thinking ISV needs cleaning, or possibly a temperature sensor is
faulty. any opinions? Thanks in advance for your suggestions!

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.
--
Ray O
(correct punctuation to reply)

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
99 Lexus RX-300
Houston TX USA

[Ray O]

Post by Ray O

Post by Steve
My wife's 99 RX300 sometimes idles very low when started with engine
warm. A blip of the throttle generally returns it to the correct idle
speed. Seems to happen only when engine is warm. My wife reported that
she often has to start multiple times to get it to idle without dying.
The car has 82K miles, and is current on all scheduled services. Two
oxygen sensors were replaced a couple months ago, but did not affect
this problem at all.
I'm thinking ISV needs cleaning, or possibly a temperature sensor is
faulty. any opinions? Thanks in advance for your suggestions!

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.
--
Ray O
(correct punctuation to reply)

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
99 Lexus RX-300
Houston TX USA

********
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.

[Steve]

Post by Steve

Post by Ray O

Post by Steve
My wife's 99 RX300 sometimes idles very low when started with engine
warm. A blip of the throttle generally returns it to the correct idle
speed. Seems to happen only when engine is warm. My wife reported that
she often has to start multiple times to get it to idle without dying.
The car has 82K miles, and is current on all scheduled services. Two
oxygen sensors were replaced a couple months ago, but did not affect
this problem at all.
I'm thinking ISV needs cleaning, or possibly a temperature sensor is
faulty. any opinions? Thanks in advance for your suggestions!

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.
--
Ray O
(correct punctuation to reply)

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
99 Lexus RX-300
Houston TX USA
********
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.
--
Ray O
(correct punctuation to reply)

I appreciate the clarification about cleaning fluids. Hope you find a
solution on your daughter's Avalon.

I am going to take a wait and see attitude for a while, and if the
problem shows up again, I'll clean the IAC, and report back.

Another poster at Lexus Owner's Club suggested cleaning the TB as
well. Don't think I'll attempt that just yet.

Thanks again,

Stephen Clark