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Ron, ASE Certified Technician
Category: Car
Satisfied Customers: 35527
Experience:  ASE Certified Tech
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Lexus RX300: I have a 1999 Lexus RX300. It has 149000 miles.

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I have a 1999 Lexus RX300. It has 149000 miles. When I climb to higher elevations, the car starts jumping,& missing. I took to the local Toyota Dealership. They said I need transmission. A friend suggested it might be the Air Idle Control. Could this possibly be correct since this only happens when I climb and not when driving on level?
Hello and thank you for you question,

The problem you are describing is not likely cause by a failing Idle Air control valve , the only purpose of the IAC is to allow enough air to by-pass the throttle plate so the engine can idle. In most cases if you have an engine misfire the computer will set a misfire code . The same thing goes for the transmission, as long as its not an internal transmission concern it should set a fault code. The problem actually sounds more like and engine misfire brought on by the fact the air is thinner at higher elevation and the can cause a richer condition. The place to start is to see if you have any stored fault codes in the computer.
Customer: replied 3 years ago.

There were no computer codes. I had this vehicle checked at the local Toyota dealership. They told me my transmission was slipping. The tranny fluid is clear and at correct level. Could it be the transmission even if no codes, and only happens at higher elevations? I have seen online that the 99 Lexus RX300 has a history of bad transmissions. Wouldn't there be a code if the transmission was slipping?

Unfortunately yes is sure could Barbara. A transmission can slip and not always show a fault code and it would be more common for it to slip under the load of climbing so they are likely correct with there diagnosis if you are not getting any fault codes. With the amount of miles you have on the transmission its is also very likely.
Customer: replied 3 years ago.

Do you think there is a danger of the transmission completely going out at any time? The cost of replacing the transmission is probably worth more than the auto.

As long as its not slipping under low elevation driving you very likely have some time but at some point it will most likely become worse and will need to be addressed.
Customer: replied 3 years ago.

Thank you so much. Not good news, but at least I know what to prepare for.


Your very welcome Barb, Im sorry I could not offer better news as well. Thank you too.
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