The EGR System tends to get restricted or blocked with carbon after 100,000- 125,000 miles which will cause an emissions test failure for NOX. If the EGR system is equipped with an EGR temperature sensor it will trigger a Check Engine Light for improper EGR flow. The repair is to clean out the EGR passages and the EGR Temperature sensor. Our technicians tell this repair is pretty straight forward and takes about 1-1.5 hours. It is also wise to verify the EGR system components i.e. the Transducer, EGR Valve and VSV Solenoid at this time.
Car problem reports
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Most reported 1994 Toyota Previa problems
The Throttle Position Sensor can get out of adjustment due to wear in the throttle body or due to carbon build up. This will cause the idle timing to advance more than 30 degrees which will cause very high HC and NOx emissions. Conversely, the Throttle Position Sensors can wear out and not properly advance the timing which causes a lack of power and poor fuel economy.
It is important to regularly check the valve clearance as the exhaust valves may become too tight. This will lead to valve failures, which are expensive to repair.
A rough idle and even an emissions inspection failure for high HC and CO can be caused by improperly adjusted valves. Also, exhaust valves may become to tight which can lead to valve failures. Our technicians tell us that regular valve adjustment inspections are a must.
A loss of power on the freeway may due to an internally leaking fuel pulsation dampener. This commonly occurs on higher mileage vehicles.
At higher mileages (125,000+) the mass air flow sensor may cause the vehicle to idle rough, run rich and even stall. It is recommended to replace the mass air flow sensor with a factory unit because the aftermarket units have very mixed results.
Usually by 150,000 miles the AC system will need some attention, especially in climates where it is used often. Our technicians tell us that it is best to service the AC system every 2-3 years. This keeps the moisture in the system at a minimum which extends the life of the components.
The ignition coil inside the distributor can fail. There will be a hesitation on acceleration, especially when the vehicle is warming up on cold, rainy days. The pickup coil inside the distributor can also fail and cause a no-start condition. There have also been some failures of the radio noise suppressor inside the distributor, which can short out. Our technicians recommend replacing the whole distributor with a complete, genuine Toyota distributor if any of its components fail.
At higher mileages, an anti-lock brake system wheel speed sensor may wear out and illuminate the ABS warning light. It is recommended to replace the sensor with a factory part and be sure to clean all rust and debris from the mounting area because the mounting distance is critical. Failure to do so may result in the new sensor setting false trouble codes.