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1997 Toyota Previa Problems
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.
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.
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.
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.
If the vehicle will not crank over, the most common problem is the starter, which tend to fail at about 100,00-125,000 miles. Sometimes it is only the starter solenoid contacts, but often the complete starter (including solenoid) needs to be replaced.
The timing chain can develop a rattling noise caused by failing timing chain guides. This is often due to extended mileage intervals between oil changes that allows the oil to become dirty and abrasive which wears away the timing chain guides until they fail. The timing chain and guides should be inspected at each valve adjustment, otherwise serious engine damage may result.
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. Be sure to check the condition and runout of the front wheel bearings on the 2WD and 4WD vehicles and the CV joints on the 4WD vehicles since worn wheel bearings and/or CV joints can cause the ABS trigger rings to rub against the ABS sensors and damage them.
On vehicles with a manual transmission, worn shift bushings can cause the transmission to pop out of gear, especially when coasting down in 1st or 2nd gear. Replacing all the shift linkage bushings is pretty straight forward and not expensive and will commonly correct this concern.
Some engines have had the problem of the crankshaft pulley bolt coming loose. This will make a rattling noise as the engine idles. Our technicians tell us that the pulley bolt should have a thread locker applied and then retorqued.
At 125,000-150,000 miles, the Brake Master Cylinder may need replacing. It is critical to adjust the brake pedal to Master Cylinder pushrod clearance or the brakes will drag and over heat.