The Toyota Tacoma 2.7L I4 engine has a known issue with the valves that if left unchecked, will cause burned valves and engine performance issues.

The engine ‘breathes’ through valves that are pushed open by the camshaft, and closed by springs. When valves are closed, they seal against a valve seat. In this vehicle, the valve seat is too soft, so after the valve contacts it thousands of times, it becomes crushed. Once it is crushed, the valve can no longer make a proper seal, and the valves erode due to extreme temperature (burnt valve).

Symptoms related to this issue:

To repair the burnt valves, the cylinder head must be removed and rebuilt, which is a costly internal engine repair, however, this issue can be prevented through inspection and adjustment of valve clearances every 40,000 miles.