At higher mileages, (125,000-150,000) the automatic transmission may not shift correctly. This can be caused by the throttle position sensor being out of adjustment or a shift solenoid needing to be replaced. Typically the transmission does not need to be completely overhauled.
Problems for specific Toyota 4Runner years:
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Most reported 1990 Toyota 4Runner 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.
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.
At higher mileages (125,000 -150,000) the power steering pump may begin to leak on the 6 cylinder vehicles and could require replacement.
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.
The 3.0 V6 engine is usually prone to leaks in the head gasket after as little as 60,000 miles. When the head gasket is replaced, the knock sensor harness should be replaced as well, as it can be damaged by leaky head gaskets, resulting in a serious decrease in fuel efficiency or in long term engine damage.
On the 4 Cylinder Engines, the Ignition Coil wire insulation is often rubbed through by the Primary wiring harness which will cause a stalling/no-start condition. The coil wire will need to be replaced and the primary harness will need to be repaired and re-routed.
At higher mileages (125,000-150,000) the input shaft seal to the power steering gear may leak. It is recommended to replace the steering gear with a quality rebuilt or new unit rather than attempt to re-seal the original unit.