The Check Engine Light may illuminate because the hydraulic valve that controls the engine valve timing stops functioning correctly. A failed engine timing valve will require replacement.Google+
Car Problem Reports
Acura RSX Check Engine Light Due to Failed Engine Timing Valve
Acura RSX Problem
Average Mileage: 72,500 mi (64,000 mi - 81,000 mi)
Check engine light and mantainence light comes on and off. I got a PO661 posible problem but don't know what it means or could be.
Visitor, 2004 Acura RSX, 81,000 mi
Check Engine Light comes on intermittently since 60000 miles. Sometimes it is off for a few weeks, but always returns after a while, and then disappears again for some time.