1998 Toyota Supra Problem Reports
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The idle air control motors tend to become carboned up at around 100,000 miles and will cause a start and stall and/or stalling at stop sign problems. Many times these valves can be cleaned, however, the sure bet is to replace the idle air control motor and clean the throttle body.
A code P0770 or P0773 may occur at higher mileages which indicates that the 3-way lock-up solenoid could be defective and may need replacement.
The rear Oxygen sensors are a critical element in fuel control (unlike other vehicles) and can cause an emissions test failure for high CO and HCs. The sensing element cracks and and reports an erroneous steady state lean condition which confuses the computer, which in turn makes the fuel mixture overly rich.
The Evaporative system may have problems with the vapor canister releasing charcoal pellets that plug the vent valve. Typically a Code P0441, P0442 and P0446 will be set. The key code is the P0446 which is a vent valve electrical failure. The proper repair is to replace the entire canister with all the valves as a unit. This is located on top of the fuel tank and is expensive. Our Technicians tell us that for awhile Toyota was covering these problems, but this may have changed. It would not hurt to call the dealer if this problem occurs to see if Toyota is still helping with these repairs.